That came from the Third season, it is old news that it (and specially that episode) is also a part of the Trek universe not fondly remembered among Trekkies.
The Thomas Crown Affair (1968).
The bank robbery is underway; in the lobby, one of the gunmen is watching an elevator waiting for the doors to open, knowing it has office workers.
The doors open, he points his gun and yells, “Get back!” Some surprised screaming and shuffling, and then:
Man in elevator: “This is an elevator!”
In Under Siege, Steven Segal is disguised as the ship’s cook. He kills someone. The big bad guy comes across the scene later: henchman in the kitchen, pinned to a cutting board with a butcher knife.
“No cook did this,” he opines.
Eh, I know what the movie is trying to imply…that the bad guy is astute enough to detect Segal’s SEAL training from the scene. But, you know, it sure LOOKS like a cook did it. It’s hard to imagine any killing that would look MORE like a cook did it. I mean, changing the dialog to “Only a SEAL would pin someone to a cutting board with a butcher knife in the kitchen,” doesn’t make the concept any clearer.
But one of the greatest stupid dialog exchanges of all time (hell, probably more than one) comes from the aforementioned Highlander 2.
Our Hero has fallen in with a no-nonsense American woman. His bizarre behavior starts to concern her, so she gives him a pretty typical ultimatum (I paraphrase here): tell me the truth, the real truth, about why you’re acting so odd, and if you tell me some bullshit I’m going to leave.
Gravely, he takes her into his arms and reveals the sort of simple explanation an independent American woman would be soothed by:
“I am from the planet Zeist and I cannot die.”
She melts into his arms and kisses him.
SERIOUSLY?
Even if true, it’s such a deadpan ridiculous thing to say in response to “don’t bullshit me!” it’s like he’s baiting her. For her to accept it immediately and without question is completely stupid, and would have ruined the movie had it not already been Highlander 2.
No less stupid is the toast Connery makes after suddenly reappearing from the dead with no apparent explanation: “Here’s to Magic!” :smack:
Another is “Lieutenant Worf! That is a very *sexist *thing to say!” :smack:
From the original Hawaii Five-0:
McGarrett orders Williams to follow up on a very tenuous lead:
“A hunch, Steve?”
“A hunch, Danno.”
Naturally, the lead pans out 110%. Nothing on TV is ever as sure as “a hunch.” 
Even this is better than the incessant technobabble on Voyager whenever a crisis struck:
“I’m shunting power from the sensors to the deflector array!”
“We need another 13 million terajoules to avoid a warp core breach!”
“Shields are down 80%! Attempting to compensate!”
The last line would be delivered after one or two phaser hits. Starfleet vessels were apparently all built by the lowest bidder. :smack:
My personal favorite is from a Lou Costello movie “The 50 Foot Bride of Candy Rock”
Lou “My wife is still growing!”
Other guy: “A woman growing more than 49 feet tall is impossible!”
Yep, let’s ignore the fact that there’s a 49 foot tall woman running around, perfectly normal.
Well, it was a comedy, wasn’t it? 
Reminds me of an exchange in the Italian biography of Leonardo da Vinci aired on PBS:
Two villagers are looking for Leonardo’s downed ornithopter after seeing it crash in the hills.
“It was a giant insect, I tell you!”
“No, it was a giant bird!”
“Ho! When was the last time you saw a bird that big?”
I kept waiting for the second guy to say “Well, when was the last time you saw an insect that big?!?” but he never did. I always wondered if that wasn’t some kind of screwup with the dubbed translation… 
First season of Power Rangers. Someone tells the heroes that the villain is a Pine-Octopus. “It has all the powers of a pineapple and an octopus!”
I wonder how many takes it took before the actor could deliver that line without cracking up.
IIRC, the above-mentioned powers meant it could emit a dark cloud and was…kinda…spiky like a pineapple.
The pilot of the original*** Hawaii Five-0***:
McGarrett’s just been captured by the evil Red Chinese. He looks up and sees the face of the traitor who set him up:
[Through clenched teeth] You dirty, double-dealing FINK!!!
Hey, this was 1968! Back then, you couldn’t say things like “Son of a BITCH!” on TV. :smack:
“Pain don’t hurt.” Roadhouse
Pretty hard to beat Plan 9 for bad dialog, especially that little opening speech by that crackpot nutter.
“Future events such as these will effect you in the future!”
Sheesh!
Criswell Predicts: “Can you prove it didn’t happen?” :dubious:
The best exchange ever:
“Oh, don’t worry about me. The flying saucers are up there. The zombies are out there. But I’ll be safe in there, with your pillow close beside me.”
“My pillow?”
“Well, I have to have something to keep me warm while you’re away. Now go on, take off into your wild blue yonder!”
“All right, but don’t forget to lock the door!”
“I’ll lock all of them … except the side door. No one *ever *goes in there!”
Sheesh, indeed! :eek:
G.I Jane “Suck my dick.”
The Room has to be the worst. Even Plan 9 is a better watch. I’ve seen The Room several times and it never lets me down.
Paraphrased line from the movie Skeleton Man:
A bunch of elite soldiers are introducing themselves:
Sniper Teacher: “I’m a sniper teacher. If I see it, I kill it.”
While holding a sub-machine gun… She ran around missing with it the whole movie, actually.
More Plan 9 thespianism:
“You have to do what you can’t not do” – Delivered utterly deadpan in a very serious moment by one of Halle Berry’s characters in Cloud Atlas
Or this, from that landmark of youth rebellion, The Way to Eden:
One.
We are one.
One is the beginning.
Are you One, Herbert?
I am not Herbert.
He’s not Herbert! We reach!
Or this tender moment from Court Martial:
Do you think it would cause a complete breakdown of discipline, if a lowly lieutenant kissed a starship captain on the bridge of his ship?
Let’s try. [they kiss] See, no change. Discipline goes on.
I’ve never seen this movie (although I’m familiar with its reputation), but now that I know about this line I want to quote it whenever I’m asked to explain what’s going on.
Probably not that many people would get it, though. 