The waitress should have left a cup, and every time you're a jerk, she hocks a loogy into it. This way you'll know how much of her sputum you have ingested.
The worst part is this jerk was prolly poor in the first place. When you get a little bit of money, you kinda don't worry about five bucks here, or five bucks there. Cool stack of unos there, big spender.