When you are playing a sport or anything competitive, and you are playing against somebody. And you or they start trash talking, giving looks, or playing tryhard and making them or you mad. And they let their anger get to them while playing in the game so they can’t focus.

To beat someone in the head

a term used as an exlamation to end a story at a random point

Pissed as a mofo and on his fucken arse

giving some one a severe beating.

When someone beats you badly in some sort of game, sport, etc. you say this

When somebody embarrasses you by beating you in a sport, game, etc...

Can be also said as, he "dropped a bucket on my head"