My boss got me left alone for a shift

My boss has been having issues with us servers slamming the salad bar. We don't mean too. Sometimes if it gets super busy it just happens. Me and one other server, Damien was on this morning to teach us a lesson my boss put a knife on the salad bar so when Damien slammed it, it went up and cut him. Not a lot. It barely broke skin but he got pissed off. My boss said "Well you should be looking down and not slamming the salad bar " Damien said since he wants to play games he's leaving and I got left completely by myself and we got hit. My boss is just immature. Like yeah we aren't supposed to be slamming the salad bar but you're seriously gonna put a knife there. I've been here 3 years and I have threatened to quit 4x. I'm getting close to just putting in my 2 weeks because I'm over childish behavior.