As Caffeine said, it's the wild west of social interaction.
Also, when you get a gander of the types of people engaged in the fighting scene (we've all seen videos), many of them seem really weird to begin with.
Get 1000 Smash players, 1000 FIFA players and 1000 Call of Duty players and I bet the Smash players act the most childish and quirky. You'll also get some of them dressing up doing cosplay shit, while every FIFA and shooter fan will be there wearing normal clothes.
I think a lot of these competitive fighting gamers take it personally like playing SF for 10 years straight mastering a couple character move sets sudden;y makes them think they are really Ryu or Chun Li. And they'll do stupid shit thinking they are invincible like a video game character.