So, yeah. This video here, from what we can see and put together from the comments, shows 2 blue belts competing in a BJJ tournament. From stand up, the guy in the white gi seemingly accidentally (although maybe recklessly) knees his opponent in the face. What follows is a cranky full-on retaliatory bitchslap from the guy who received the knee and then a lot of pacing and sulking.
The video has about 23,000 views now - that's über insane viral by BJJ standards. It illustrates how much we all enjoy a quality slap in the face, even in the BJJ tourney setting.
Here's my take on this, in brief - slapping an opponent is just bad form. If I had a dollar for every time I've been kneed or otherwise smashed in the face while training (by elbows, heads, heels, etc.), I'd have at least $1,000 by now. It's a rough sport, and stuff like this happens ALL THE TIME. Recklessness should be avoided and everyone should make every attempt to avoid accidentally striking opponents/teammates, but it's still going to happen. Retaliate like this (and videotape it) and ne'er-do-well (and super cool) grappling websites will put it on the internet and mock you.