I always thought it was, “when his pants ARE too tight in the seat”.

At the risk of analyzing this way, way past the point of ridiculousness, I hadn’t even thought of it that way (that Smails was referencing a fat wallet, which would make one’s pants tight, so it’d be hard to smile without tight pants) but that’s an interesting take. I always thought (per the way I heard it) that the joke was about how corny Smails is: he thought talking about somebody’s “seat” in his last line was clever and edgy but it’s really just about the lamest line ever uttered.

Now I can’t tell which approach I like more – “aren’t too tight” is actually kind of a smart line, but it still works because laughing about something like that makes Smails seem like a prick; “are too tight” works because Smails is being corny. Given that Smails is corny AND a prick, sounds like both work. I’ll have to check out the movie when I get home and see if I can tell which one it is.