Tip Profiler
Someone who checks up on the size of the gratuity left by another person in a restaurant, bar, etc. to make sure that person didn't short change the waiter.
I picked up the tab at the bar. When I was looking away, one of my freinds grabbed my credit card slip to make sure I had left a big enough tip. So I said, "Dude, you're a tip profiler? You just tip profiled me!? Next time you're paying A-hole!"