I think there's a line between being an ******* and not tipping. The family was going out, and using the money the OP would have given them, could have bought something. Maybe a pizza sounded good to them, and since the family was going out anyway, they thought they'd get some. Nowhere did the OP say they didn't have food or water for the day.
I would never expect a tip with that job, but if someone is a complete knob about simple requests that would in no way place a burden or cost them more money, I'd get a little pissed.