Touch a server
Making physical contact is one way a server will endear a customer to them and thus milk an extra few percentage points on a tip, but that subtle shoulder brush is a one-way street. Any self-respecting adult knows that personal space is a right, not a privilege.
Order a well-done steak
Every time a steak is ordered well done, the state of California cries a tear for the thousands of gallons of water it took to raise a perfectly marbled, horribly charred cut of beef.