Is there policy on intentional beer throwing at people?
Edit: I thought it was funny because of how "epic badass" the OP was trying to come across, plus the absurd lengths the commenters went to defend obvious antisocial behavior. Remove your reddit brainworms! The joke is not someone wanting their girlfriend to not be harassed, the joke is Reddit
Honestly screw it, I don't think the OP is really funny anymore, either. They might come across as silly due to being angry but who doesn't? Plus they're vegan, so, 
Yeah the reason the original post is funny is because of how much the OP is trying to come across as some cool badass, not him getting angry about people harassing his girlfriend. As such the other primary reason it's funny is because the commenters are tripping over themselves to defend absurdly antisocial shitty behavior so they don't have to be critical of their glorified rock concert. It's just a case of both kinds of weird redditor misogyny ("I must beat people to protect MY WOMAN" AND "women don't deserve rights") at the same time
On the other hand I'd probably react the same if someone did that to my partner so I'm having second thoughts about the original post being funny at all, obviously people don't get why the comments are funny and think I was just mocking this normal request from a dude by itself and jumped in. For those in the back: THE JOKE IS HOW ABSURD IT IS TO DEFEND THROWING PISS