I don't mind quitting because someone is upset about losing, it's completely natural, although, I really don't think its nnessisary to start calling names and being a totally bad sport about it. It's still something easily shrugged off.
What I dislike is when people are inconsiderate of a duel or they give their word, and leave a game suddenly because they are upset. It totally ruins everyone's day because the mad person can't handle playing fair. Not to mention it's extremely childish.