It's not until after he's pulled the whole thing off that Jason realizes what a stupid move it was.

Jason raises his eyebrows. "So we like… spar? And you'll what, let me fuck you if I win?" "Sure. If you win." Tim smiles and a thrill goes up Jason's spine. He shucks off his jacket and shoes before making his way to the mat. "It's a deal, then. Hope you won't regret it, Replacement." Tim's teeth look strangely sharp under the Cave lighting when he says, "I'll try my best."

“Bring me the Joker’s head on a platter,” Jason says, and he doesn’t mean anything by it, not really. It’s the kind of thing he jokes about when he’s overwhelmed, and he’s overwhelmed by Tim a lot. Tim’s intensity makes Jason turn flippant, makes him counterweigh the seriousness with comments about his own torture and death, like that will somehow lighten the mood. Jason says all kinds of things, for all kinds of reasons. He doesn’t expect anyone to listen.