Lyric discussion by deviationer 

Cover art for Uncle lyrics by Mindless Self Indulgence

So if this is about a bully to his victim, I don't get the "Why don't you say it Uncle" thing.

Is the bully pretending the victim is his uncle who abused him?

"Saying Uncle" is like sayign "I give up!" So, he's basically saying Why don't you say you give up, give in, etc.