There was a showing of the movie where I live this past Saturday around midnight. I'd already seen it before, but seeing it with a bunch of other people who were "in on the joke" was a good cult movie experience. Some of the gags:
1. There was a "best friend" count. Every time Mark or Lisa mentioned Mark and Johnny being best friends, the count went up. Think it got to 8.
2. Half of the scenes where Mark showed up, a bunch of people called out "Sestosterone!" - because his actor's name is Greg Sestero.
3. Every time a picture of a spoon showed up in a scene, a barrage of plastic spoons were thrown at the screen by viewers.
4. Everyone joined in on the big quotes; "You're tearing me APART, Lisa!!", "Stop ganging up on me!", etc.
5. Making puke noises during the sex scenes.