This is an oldish thread, but I feel like responding.
The funniest anime moment I've ever seen was in Slayers Great. I was staying the night at a friend's house back in high school, it was around one or two in the morning, and we were watching this movie. To this day, the chibi gollum version of Lina Inverse brings me to my knees. I find it to be the most hilarious anime moment ever. From the noises the gollum made to the way it fell over and wasn't able to get back up. It was just perfect.