After another second or two, Jason clears his throat quietly and tries to put on a more neutral expression, but there's one more private-but-still-visible-to-Batman grin as he starts walking again.

"Yeah, I've met that guy. Not in a bathroom, though." So this is what it takes to make Jason converse like a normal person. A comparatively normal person. There are more things he could say — it's obvious he knows 'that guy' better than only having met him — but he remembers that into-the-abyss look Bruce had a few minutes before. They've probably stared into it enough for tonight. It's not hiding stuff if they both know Bruce can tell, and if they both know Bruce doesn't really want to know. It's what it is: alternate histories which can be discussed if they really want, but also left alone.