Why is it irritating when someone copys you?

Because you feel like they're stealing your idea and that people are going to think it's their idea and they're going to get credit for what you did, and even worse, people are going to think you copied it off them.

Folk, I see you try'n'a do it like me
Man, that dance was ugly

Copies!

"Imitation is the highest form of flattery"

Because it means they have no life of their own and yes it is irritating and boring.

I find it flattering when someone copies me. :-)