I always deadpan people who say that, make my index/middle fingers to form a V shape, then force the corners of my mouth up.

You want a smile? Go find someone who’s happy. You want service? Don’t tell me what to do and I’m willing to try and help.

It usually got a chuckle, but sometimes the person would get uncomfortable and leave like they think I’m about to stab them or something.

Or I tell them my grandmother died.

Hey now we can both be uncomfortable and wishing you hadn’t said anything!