I was wearing my “Faber College, 1963, Phys. Ed” T-shirt today, and the checkout guy at Trader Joes called after me as I left and said “Hey, is that shirt from…”
Animal House
And I smiled, and gave him a thumb’s up.
I probably wear this shirt once or twice per month, and he’s only the second person to get it.
But, I love wearing it, just for this reason.
Why are inside jokes so great?
It shows you “belong”.
Yeah, this.
But also, one of the ingredients of humor/jokes is The Unexpected (yet oddly appropriate). If you meet an inside joke, outside of its native context, you increase the Unexpectedness.
Everyone yearns to be a part of “Us” in the perpetual “Us” vs “Them” conflict. In-joke are a signal that at least in that one particular instance, you are one of “Us.”
Had a pizza delivered, once, by a guy who recited a pizza delivery poem that was a take-off of the Green Lantern Pledge. We both smiled over it and I of course had to overtip him. He seemed surprised and pleased, but a little abashed. Then I said, ‘hey, I got pizza with the Green Lantern Pledge; how could I not tip?’ He nearly went ecstatic. He said I was only the second person ever to recognize the pledge.
Made both our days.
A couple months ago, I saw someone wearing a T-shirt with the Cerberus logo on it from the Mass Effect series. We had a nice conversation.
Exactly this.
I made up a t-shirt for “St. Thomas Franciscan University.” So far, a couple of people have gotten the joke. (“STFU – Shut the F— Up.”)
There’s this guy who’s an IT consultant for a firm that we work with. He’s developed a couple of applications for my department and we see each other say 10 times a year to improve some stuff and add other stuff.
About two years ago, we were in the final stages of development of a new program, summing up how things were going to look like once we started working with it for real and I said: “OK, but I have got a question” and he muttered “42” under his breath.
I looked at him and went something like 
.
We’ve had interesting conversations since then.
I agree with this general sentiment. It gives us something in common. It also makes us feel understood. I love making random references, sometimes I forget that they’re things that likely most people won’t get and it gets me into a little bit of trouble. Other times I make a random reference not really expecting anyone to get it and they do. I’ve learned to just let some of those sorts of things slide when they’re not gotten.
I also think it makes us feel clever. Almost everyone will get a reference to some major pop culture thing. But if someone makes a reference or gets a reference to something more obscure, it makes the person who made the reference feel good for making an effective reference that someone else was able to discern and appreciate and similar for the person who gets it, that they were able to figure it out and the other person also appreciates it.
As a metal fan, I often wear band shirts with the hope that someone will either recognize the band and either strike up a conversation or at least give a knowing nod, or will think the shirt is cool looking and ask about it. In fact, I try to make a point of not just wearing a random one, but picking one that will be appropriate for wherever it is I’m going. I actually tend to do pretty well with people specifically commenting on it too. If I’m at a concert, I usually get away with a more obscure or special shirt and I almost always either get approached based on it or it comes up while talking to someone. As an example, last show I went to, I made a point of picking a band I was fairly certain was influential to both of the bands I was there to see, and while chatting with one of the band members, he directly mentioned how much he loved the band. Other times, it’s people who may have no idea that it’s a band shirt or, maybe guessing it is, no idea that it’s a metal band, and it affords me an opportunity to just talk about something I’m really passionate about. It’s WAY more interesting to have a conversation with a stranger about that than some random small talk nonsense like the weather or sports.
It definitely strikes me as the same sort of phenomenon and sense of satisfaction as an inside joke, it’s just not funny.
This lawn supervisor was out on a sprinkler maintenance job and he started working on a Findlay sprinkler head with a Langstrom 7″ gangly wrench. Just then, this little apprentice leaned over and said, “You can’t work on a Findlay sprinkler head with a Langstrom 7″ wrench.” Well this infuriated the supervisor, so he went and got Volume 14 of the Kinsley manual, and he reads to him and says, “The Langstrom 7″ wrench can be used with the Findlay sprocket.” Just then, the little apprentice leaned over and said, “It says sprocket not socket!
I love Steve.
Why are inside jokes so satisfying?
Because it’s too dark to read.
Got it in one, WordMan.
Disclaimer/Attribution: The joke was from Steve Martin.
Dude! Don’t tell anybody!!!
We knew. 
I have a Rolex watch tattooed on my left wrist. The time is set to 4:20.
You can almost predict who will “get it”.
Rolex. 4:20.
Sigh. I must not be one of the cool guys.
The time Lincoln died, right?
These kinds of public inside jokes depend on two things: The in-group knowledge as everybody above has amply explained, and your audience being observant.
Using kayaker’s 4:20 Rolex example, hundreds of (ex-)stoners kayaker encounters in daily life know what 4:20 means. But how many of them will pay enough attention to **kayaker **to A) notice the tattoo, B) recognize it’s a watch, C) read the time, D) make the connection, and E) says something or at least smile knowingly? Damn few IMO.
Folks who are observant themselves like to put out these little tests to catch other observant folks. That’s a separate in-group and is rarer than metal-heads, Steve Martin fans, stoners, pun fanatics, etc.
Most of us like to be the center of attention at least some. Wearing your little attractive thing, whether it’s a tattoo or a band t-shirt or saying some catchphrase, is an attempt to say: “look at me; I’m special. Pay attention to me.” In a coded way that only other cognoscenti will respond to. IOW, it’s stealth bragging and there’s nothing much wrong with that.