Having been unknowingly ROBBED in narrative by the ability to say something exactly like that, Liam makes change without looking at the register and 'hehs' a little in response to exactly how much Slurpee is ever too much for anyone. "Yeah. You know a three letter word for 'adjustable dress feature'?"
So ...he could have picked a more dangerous question to ask, but it's possible that question really would have had to have been 'will you blow me under the counter,' or similar.