Don’t Tip Your Waiter
Here are two definitions in conflict with eachother based on the derivative meaning of their root:
gratuity : something given voluntarily or beyond obligation usually for some service; especially : TIP
gratuitous 1 : done or provided without recompense : free *2 : not called for by the circumstances : unwarranted
Therefore, it is impossible to provide a gratuity while being gratuitous. My use of language extends beyond me, 20% is appropriate, but not if the waiter rushes you out and doesn’t offer you more chips and salsa as you were surprised that this was the first Mexican restaurant (Taco Bell not included) where you walked away unsatisfied.