Maybe the guy's action of making deer horns violated some important rule or caused harm in the cartoon world, so the character shot him.
It could be that the cartoon guy is having a bad day and takes it out on Bugs Bunny. Or perhaps he's been ordered to do so by a villainous character.
Maybe he's just being naughty and doesn't know it's wrong.
It could be that he has some kind of mental issue or was influenced by something negative in his environment. But seriously, shooting a cartoon police is a really odd and inappropriate thing to do.
The cartoon guy might take the antlers off because they are damaged or it could be a symbolic act in the cartoon to represent something deeper about the character or the situation.
Maybe he was under a lot of stress or had some kind of mental breakdown. That could cause him to act so strangely.
Well, it could be that the girl was defending herself from a perceived threat. Or perhaps it was part of a crazy and unexpected plot twist in the cartoon's story.
Perhaps the cartoon was trying to show extreme emotions and their consequences. The girl's jealousy might have built up to the point where she acted in this violent way without thinking about the consequences.
Maybe the small guy was defending himself or had a grudge. It could be a complex situation.
Maybe he wants to play a prank or get something secretly without being noticed.