A slight deviation from the trip recounting. A scientific exploration into your sexuality

I don't get straight man humor.

Background: I saw Pineapple Express last night and I thought it was good. I was pretty much laughing throughout the whole first half, but then...

One scene that I did not find really funny, which the rest of the theater (mostly dudes) found hilarious was the one in which the two straight male leads mimicked gay sex to get their ropes off (they were being held against their will and the act of rubbing ones ropes on the other's belt buckle could save the day).

Resulting question: Can anyone tell me why straight men/boys find it hilarious when other straight men are put in gay situations? I don't mean to seem uptight, and it's not like I am saying "This is no laughing matter," but I just don't see what is so hilarious. I mean the dudes in the theater were busting a nut. And it happens all the time. What is up?