The thing is, Loki can behave very well when he's asked to do something he wanted to do anyways. Sure, he could be a brat just for the sake of it, but he really wants to get his hands on Phil, see what makes him loose his conposure. He can see hints of it in the way his breath is slightly quickened, his erect cock so tantalizing close to Loki's lips. It's just enough to make him want more.

He starts by flicking his tongue out, dragging it through the smear of precome, before taking the whole digit into his mouth. Loki begins working over the thumb; moving his head, hollowing his cheeks, closing his eyes and humming as if it were a spoonful of delicious ice cream.

He gets so lost in it that he briefly forgets himself and brings a hand up to gently touch Phil's wrist. Quickly, as if burned by the realization, Loki's hand snaps back to his thigh.