Is it rude to tell someone they're being rude?

This was prompted by a story my husband told me. The other day he went to a liquor store. The parking lot isn’t very wide. There are about 10 parking slots, at an oblique angle across from the building. Well, some guy parked his big old truck directly in front of the door instead of in a slot across the parking lot. Between that truck, and the cars parked across the lot, there was no room for anyone to go through the lot. They couldn’t get to the parking slots, couldn’t go around to the drive through.

Rick was one of 4 cars that were backed up to the street, waiting for that moron to put the beer and ice he’d bought into his truck. He was taking his sweet time.

Rick said the driver of the first car that was waiting got out of his car, walked up to the guy and said, “Are you an idiot???”
The idiot guy got defensive, of course, and said, “No!”
The other guy said, “Can you not see these cars backed up behind you because you’re blocking the whole f***king parking lot with your truck parked the way it is and no one can get around you!”

The idiot guy just started mumbling and snarling to himself and got in his truck and drove away.”

Who was the rude one? I agree, the guy who clocked him could have done it more nicely, but even if he’d just said, “Hey mister. Could you move your truck, please? No one can get around you.” it still could have been construed as “rude.”

Is it rude to ask a person to stop talking through a movie?

Is it rude to ask a visitor to stop playing and texting on their phone when they’re supposed to be socializing with you and the others?

What is “rude,” anyway?