Yo head so big I can skate on yo head.
I'm talking bout real real big, set a plate on yo head, charge a phone on yo head, build a home on yo head, studio wide, write a song on yo head.
Alright, listen up, you smooth-brain. This joke is all about exaggerating how HUGE someone's head is! Like, so big you could build a whole freakin' STUDIO on it. It's called an insult joke, but it's so over-the-top it's kinda funny. But, like, you probably wouldn't get it unless I spelled it out for you.