Do you think it's okay if I serve caffeinated coffee to everyone who asks for decaf?
Why do you give caffeine to people who don't want it?
They were all rude.
I know that it can be frustrating dealing with rude people, but what you did is wrong. Just because someone is rude doesn't give you the right to intentionally give them the wrong order. Giving someone caffeine who didn't want it can potentially really ruin their day and night if they can't sleep after.
Nah
Just because it's something small doesn't mean you can modify orders like that. Customers order things specifically for their needs, so don't you want to follow that and do well in your job? How about you come clean to your boss, they would appreciate your honesty because everyone makes mistakes.