Debate from my workplace (I am not Person A or B, nor was I present):
Person A and Person B are eating lunch together. The waitress brings their order. Person A comments to Person B that the waitress messed something up about his or her order. When the waitress returns two minutes later to see how everything is, Person A lets her come and go without saying anything. Person B then interjects and says something.
I generally agree, but if I'm Person A and they're going to passive-aggressively grumble about it the rest of the meal or let it affect their mood otherwise (yes, I should probably steer clear of those people in general), I'll interject.
Problem could have been easily solved by Person B asking Person A if he/she thought it was worth bringing up to the server immediately after Person A first complained.