And how does that make anybody's life better? Besides giving yourself an undeserved ego boost, that is. So the guy called him a pussy. Big fuckin deal? Are you really that afraid of being unmanly that you need to violently suppress anyone who suggests you aren't manly? Do you really even care about anything strangers think of you? And do you think you'll improve a stranger's conception of you by beating the snot out of him? It would just give him a legitimate reason to hate you, and he might then want to get revenge on you, starting an endless cycle of reciprocal hate, all because you needed to feel a smug sense of superiority. Do yourself a favor and leave potential enemies out of your life wherever possible. You'll have a more satisfying existence that way.

If you really feel you must do something, how about trying a witty comeback?

Annoying asshole: You're a pussy!
Me: Hey, you are what you eat.