The gag reel (recently taken down by Disney), seen on Youtube (via MTV Geek) is loaded with great laughs, from Agent Coulson's goofy demise to Robert Downey Jr. and Mark Ruffalo's lab-related gaffs (the two previously shared the screen in David Fincher's "Zodiac"), the clip includes a few favorites:
Robert Downey Jr. and Gwyneth Paltrow's Awkward Goodbye Kiss - The two have starred in both "Iron Man" films, and are both notoriously funny and affable folks, so goofing around on-set is surely something that happens often with them around.
Jeremy Renner's "Trek" Moment - Jeremy Renner, who plays Hawkeye on the film, during the pivotal battle for New York at the end, jokingly refers to feeling like he's on "Star Trek" with his communicating between heroes. He even goes so far as to potentially ask for the current stardate.
Costume Issues - Both Robert Downey Jr. and Chris Evans (playing Captain America) seem to struggle with their outfits at different points. Downey has issues with his Iron Man helmet, while Evans can't seem to get his parachute on, mid-flight.
Mark Ruffalo - Mark Ruffalo has plenty of great moments in this clip, including knocking over props, having a tender moment with a stuntman in a motion capture suit and just generally joking around with cast mates. However; his funniest moment comes at the end of the clip, where he runs away from the final battle against the Chitauri invaders.
All in all, a funny gag reel that hopefully finds its way to the DVD and Blu-ray versions of the home release (due out on September 25, 2012).