You'd think that but... [He catches the rock on the back of one hand, lets it roll up the arm and across his shoulders before it rolls up his other arm and goes flying high into the air. And now that he's got time to boast...]

Do yooouuu have a firebender for a brother?

[He pauses for a second, a blank look coming across his face instead of continuing on with the phony "you live with a firebender you learn to take the heat" speech he was preparing.]

Wait... do you have a firebender for a brother?

[And because of that momentary lapse of concentration that rock that was in the air? Yep, not in the air so much anymore. It's more on the ground now... after bonking Bolin on the head.

After yelping in pain he growls and stomps the rock down into the ground with one big movement and rubs his head vigorously.]

Immunity to rocks not withstanding.