He feels an open summons and lets it grab him -
"Well, this conversation just got way less cute," remarks Tony. She looks over the pile of things Cam made to verify that it contains all of the things.
"Yeah, I think I'd like to take my stuff and go. No offense to you guys and your murder conversation."
So he just... concentrates on her going away...?
Cam is looking peeved at the Joker.
And poof goes Tony, with all her stuff.
"Are you really that deprived of entertainment?" he asks the Joker.
"Mm, you got a point there, Johnny." He flicks a glance at Cam. "No promises, though."
"Oh, come on," John groans. "Are you really so married to your principles that you're gonna make me translate everything you say because you can't come down to our level and talk normal person English for five minutes?"
John turns to Cam. "Do you want me to explain him?"
"Could be useful."
"Fine. Okay. So our friend here," he gestures at the Joker, "has some kind of philosophical objection to promises. As far as I can tell, he just doesn't make them, and if he does, he's probably lying about something. Or kidding, for his very special definition of kidding. But if he goes as far as to actually say 'no promises', that means he would be promising something, if it wasn't against his quirky cynical self-obsessed religion. It's sort of the closest you're gonna get."
"So, 'no promises' means 'insert counterfactual promise here'."
"Yeah. Except when it doesn't. But this time it did."
"How did you learn to interpret this, exactly?"
"I've been getting a lot of experience this past week."
"And you're naturally talented," the Joker chirps.
"So in your talented-amateur opinion, I have what from a normal person would be a promise that he's not going to do anything so appalling as to make it worth prematurely going home to stop him. Is that the size of it?"
"Yeah," says John.
"Okay, cool. Is there anything else I should be doing here before I go - hmmm, 2012 - patch your ozone layer and feed your Somalians and cure colony collapse disorder and refill some aquifers and stuff like that?"
John glances at the Joker.
"Nah, we're all set to handle things from here," he says cheerfully.
"Okay. If I want to go back sooner than eight years from now, or if it seems that in eight years you have forgotten about me, where do I find you?"