oh so you think its ok to rip his ear.in that case let me grab and rip your balls let me k...

He doesn't have to know if he likes it. He'll tighten up.
Just about everywhere, but he'll tighten up. and that'll be a decisive sign for his pleasure. Or yours. Always so damn hard to distinguish in yaoi-land.

Really not my place to light this torch, but god this trope...
"He's tightening up, he likes it!"
well my dude, he's also suffocating and turning blue, but who am I to point that out.

Or "I couldn't help myself."
Good Sir, I am also losing control over here. Don't mind the baseball-bat.