b3ta.com has a collection of what they call heckles but I think are more accurately descirbed as wise cracks, as heckles are generally directed at performers.

There is some of that, but they aren’t the best ones. The best ones are those that come from no where, from a stranger. My favorite was submitted by a fellow named Furnes. I’ve taken the liberty of reprinting it below.

In GCSE history for some reason we had to watch Kennedy getting shot. I never understood why, since we were learning about Russia at the time. Maybe the teacher had the decorators in or summat and just wanted to see a man die. Anyway, just as his cranium explodes in a shower of brain, blood and bone, Chris shouts in his best Southpark voice “Oh my god! They killed Kennedy” immediatly followed by the entire class shouting “You Bastards!” We never got to watch videos after that.

You can read them all but be warned, there is quite a bit of language.