I think that’s probably a rather more narrow definition of threadshitting than the one in common application and (for example) I’ve been accused of it (not by a mod) when there was no actual ad hominem, just that I answered in a way that questioned the wisdom/validity of the topic/proposed action.
(Interestingly, I used the head-drilling analogy there too - almost word for word - I had no idea it was so ingrained in my mind).
At the risk of flagellating a moribund equine, I’d like to see a bit more discussion of the side-issue(s) I tried to raise in Post #16.
Specifically, I’d like some exchange of views on what distinguishes threadshitting from just plain old hijacking. The reason I ask may be perfectly obvious to anybody who has been in a thread where I have posted. No matter how serious the issue, as often as not something somebody else posts will cause me to respond to the content of that post even if it itself is tangential to the “main topic.” And if there is follow-up to that sidetrack I may help the sidetrack along to the point that the Hijack becomes the thread’s main issue.
I have tried to allay such disruptions when I sense the issue would be better addressed in a separate thread by starting a new thread and providing a link to the thread that spawned the idea. However, as often as not, that new thread will just fizzle out with few (if any) comments while the parent thread goes on its merry way. In that case (those cases) I’d have been better off to go ahead with the hijack of the original thread.
This, of course, presupposes that the hijack I had in mind was even worth discussing at all.
But, as you can see, adopting the notion of inserting a side-issue into an existing thread (as this post is attempting to do) runs the risk of being seen as threadshitting where all I mean to do is provide what I see as a hijack that I (at least) see has some relevance.
Saying it another way, what’s the threadshitter to do to modify his or her behavior if all he or she means to do is to have a little hijacking fun?
And said a little more pointedly, how many of us posting in this thread will see ourselves as threadshitters? Is threadshitting purely in the eye of the threadshittee?
But is all threadshitting bad, even as defined by Dex? Wouldn’t the general consensus, for example, be that Elucidator’s contributions, however belittling or sidetracking they may sometimes be, are witty and urbane?
That would not be the right answer. The choices put forth by the OP are “spade” and “auger.” Only one of those can be the right answer.
Now the moralistic answer, that’s another story . . . 
Back to the topic at hand.
Do the men who shit on the ramparts leave the toilet seat up or down? That is the important question which must be discussed and answered.
I’m sure some people consider any hijack to be threadshitting. What I consider threadshitting, tho, was what used to happen in ENT Episode threads. Every week, someone would just have to come in and inform us all of just how lame Star Trek is.
Now, if we were just having a general discussion of Trek and someone did that, I didn’t care much (tho I might have still thanked them for their impressive superiority). But to come into a weekly episode thread, which is OBVIOUSLY a fan thread, to label us all as tards is threadshitting. Applies to all sorts of threads, obviously, but that frequent experience is what comes to my mind when we discuss threadshitting.
Same with religion threads, imho. If someone asks a question of a certain religion’s view or practice of something, I consider it threadshitting for certain selfrighteous atheists to come in and loudly proclaim that the thread is worthless because the Invisible Sky Faerie doesn’t exist. That is right up there with the very height of rudeness.
I tend to agree pretty much with your distinction, NoClueBoy, and if the need arises to label some off-topic post or comment as being either a hijack or a case of threadshitting, I’d probably reserve the latter for some seriously negative and hostile wording. I’d also add that it would depend a good deal on the theme of the thread. In some threads where the level of discourse is already heated and adversarial it would take a greater level of vitriol to be taken as threadshitting, where in a much more civil and easygoing thread just a moderate level of venom would qualify.
Is it possible to accuse somebody of threadshitting in a Pit thread? Would such accusation be taken seriously?
I’m on board with that. The character who comes into every discussion of a reality show to announce, always without any evidence, that every aspect of the show is scripted is similarly a threadshitter. However, this would not be threadshitting in a thread about “What do you think about reality shows?”.
[aside]
So, my question is: What did we call it before they coined threadshitting. And can we go back to that? Fascination with toilet references is so pre-school.
[/aside]
*No matter how serious the issue, as often as not something somebody else posts will cause me to respond to the content of that post even if it itself is tangential to the “main topic.” *= not a hijack
And if there is follow-up to that sidetrack I may help the sidetrack along to the point that the Hijack becomes the thread’s main issue.= a hijack.
*However, as often as not, that new thread will just fizzle out with few (if any) comments while the parent thread goes on its merry way. In that case (those cases) I’d have been better off to go ahead with the hijack of the original thread.
All IMHO. 
Nope - it’s a false dichotomy as presented - just because someone offers you two choices, it doesn’t necessarily mean that’s all there are, or that the two they’ve offered you make sense. Have you stopped beating your wife yet, or not?
I’m just saying those are the choices the OP seemed to specifically want to talk about in the thread he/she started. I was trying to be a smartass and answer in the spirit of the riffs that were going on in this thread about thread shitting. Your response (according to all I’ve read) wouldn’t be threadshitting but it would, in a sense, be veering off-topic.
I realise you were speaking somewhat tongue-in-cheek, but anyway… when people ask non-rhetorical questions, they are by definition not in possession of the full facts, so it’s quite possible for any choices they lay out thinking they’re covering all bases to actually cover no bases at all - sometimes the correct answer to the broader question is to point out that the premises on which it is based are incomplete or incorrect - or in other words, sometimes, the answer to “is it A, B or C?” is “no, it’s not any of those”.
I do appreciate that this might not qualify under everyone’s definition of threadshitting, although it certainly does for some people.
FWIW, here is a thread I started about this topic a while ago:
Okay, here’s my opinions:
Threadshitting - When a poster says that a subject has no possible worth as a topic of discussion. It is possible to trash a topic without threadshitting, if that’s the subject of discussion. For example, if the OP is “What’s your opinion of Major League Baseball?” then a response like “I think baseball is the most boring waste of time ever conceived by the human mind” is a legitimate response. But if the OP is “Who do you think will win the world series this year?” then the same response would be threadshitting.
Hijacking - When a poster attempts to change the subject of the thread. If the OP is “Who do you think will win the world series this year?” and you turn it into a discussion of who will get voted into the Hall of Fame this year, then you’ve hijacked the thread, even though it’s a legitimate topic on its own merit and the discussion of that topic is respectful. The proper thing to do is start a new thread on the new topic and allow the original thread to follow its OP’s topic.
Trolling - When a poster says something with the intent of causing an argument. It can be an OP or it can be a post in an existing thread. In this board there are few topics which can’t be discussed at all so usually trolling is defined by how a post is worded.
TMI aka Too Much Information - A post on a subject that some people do not want to read about. It’s more generally used as a warning to others rather than as a form of offense.
Ad hominem attacks - Saying bad things about the poster rather than the contents of the post. If my response to “I think baseball is the most boring waste of time ever conceived by the human mind” was “Millions of people enjoy watching baseball so obviously it has some entertainment value you’re missing” that’s legitimate. But if my response was “The only people I know who don’t like baseball are Communists, so what does that make you, Comrade?” I would be attacking the poster rather than the post.
Non sequiturs - A form of hijacking or threadshitting. It’s when a person posts things which are completely unrelated to the topic of the OP. The implication is that the OP is so worthless that nobody is even reading it to find out what’s being discussed. An example would be if I responded to “Who do you think will win the world series this year?” by posting “Lovely weather this time of year. Is it raining where you are?”
I’m going to pass on 6, 7, and 8.
If you take a look at post #131, you’ll see a perfect example:
http://boards.straightdope.com/sdmb/showthread.php?p=8841595#post8841595
Can this thread really have gone on this long? Jeez, whatta buncha morons. Get a life, will you?
P.S. Hi Opal!
Okay, fun’s over, move on, nothing else to see here.