we were having so much fun, until a man gave him a dirty look, he then tried to control himself... it was weird to me. but i felt bad for him. I didn't know how to help him, how do i do that next time if that does happen again?
Assuming you want to see him again, this is something you should discuss to get a better idea of why it was of concern to him. If you don't plan to see him again, don't worry about it.
Just be like, "Hey are you okay?" Or give him a warm smile and say "Do you want us to leave?" Just go somewhere more comfortable and ask him if he's okay.