Restaurant tipping aside, there's a couple people I always make sure to take extra special care of: bartenders and delivery people. Why? Because they remember who tips well. If a bartender sees two people waiting for drinks and one person always tips a buck and change while the other person doesn't tip, guess who is going to get their drink first and probably doesn't even have to remind the bartender what they want if they are that good? Same deal with deliveries, even moreso. Drivers seem to get stiffed a lot more so if they are making a run and one person tips especially well, guess who gets bumped up to the first person to be delivered to?
"I've found that when you want to know the truth about someone, that someone is probably the last person you should ask." - House