"Oh sure. How's this pose?"
By which I mean: respond as yourself. Acting like a jerk to strangers because your character is a jerk is not a cool thing to do. If you'd like to say no to the photographer, that is absolutely fine. But if you don't mind the photo, talk like a polite human being. Save the RP snark for joking around afterward.
Tom Petty [Final Fantasy XV] (9%)
Bondage Finch [Bondage Finch Adventures] (12%)
Your Mother [Debbie Does Dallas XXIII] (8%)