He's either masterfully hiding his jealousy now, or he's so far in denial about it that it may as well not exist. If he can fanboy over Bruce and Catwoman, he can totally fanboy over this ship, too. And besides that, the logic is so sound and reasonable that a ( secretly ) smart guy like John can't bring himself to be too upset about it. It's fine, everything's good, so what if Oz took Riddler's coat? Those explanations were all perfectly good and sound and... good.

"Right, yeah... that," he agrees, slightly awkward. "Well, hey... any buddy of yours, and all that stuff. If I can do something, ya just gotta say so," and John is a murderous little psycho but he does mean that honestly. This city doesn't even try to hide how unjust it is, so he's more willing ( reckless, even) in offering his help to any poor soul ( brave enough to approach him ) with a Sub tattoo. Especially rivals new friends.

"Ooooh okay, okay, I get it... it's a secret date," the devilishness of his grin and the following eerie chuckles underline the jest; he understands ( probably? ) he's just pretending not to, because hijinks. It's a pretty convincing idiot act though, and he doesn't often demonstrate his skill at putting it on and taking it off at whim but, these are his dearest buddies, after all. They already get it. "Are you gonna bring flowers? Chocolates? Better not show up empty handed, that's just impolite."

He just so happens to shift to get comfortable with his basket of mysteries atop his lap. Obviously just a random, thoughtless motion.