Just give them some space until they cool down, then go talk to them again. Try not to ask about what that person was having problems with. If they want to get it out of their chest, they'll do it themselves. Just be there to listen if they do, and don't judge them since anything can happen to anybody. In the case they insist on being rude or some shit, just don't be the same as them. Show them that you're civilized and level headed, and that will put them to shame harder than any insult.