From this interview:

Q:But we’re agreed Hulk had it worst?

Ruffalo: Walking on set with my little leotard was particularly humiliating.

Hemsworth: One of the funniest things — I don’t know if this will be an outtake — but there is a scene where we all turn to Ruffalo and Black Widow (Scarlett Johansson) says, “Now might be the time to get angry.” Normally he Hulks out and kills a bad guy. But in one take, Mark yelled (an expletive), ran the whole length of the set and dove into a car.

Ruffalo: It was a big beast coming.

Hemsworth: He was in the leotard. That was the funniest thing. It will be the opening of the DVD extras.

Ruffalo: The first day of the leotard I said, OK (expletive), get a good laugh. Let’s just get it out in the open. There was a lot of snickering and off-color jokes about the leo part of my tard. I don’t think that needs explaining.

ROFLAMO. I’ve seen photos of Tony and War Machine in their CGI gear for iM2, but not much for the Avengers yet and definitely not Ruffalo in a leotard. Please someone tell me there are pics of him and I don’t have to wait for the DVD???