Some people are too sensitive. Someone described an incident where a child was backing up with a shopping cart and when she said “Watch out,” the mother complained she was rude. She could have said, “I am walking behind you. If you back up, back up without looking, you may be hit by my cart. Please be careful.” By the time she said that, the damage might be done.
It is more important to issue warnings promptly than politely. Rudeness rarely accomplishes what one wants it to. Most people are not going to think, “He was rude. I deserved it.” They are going to stop at the first sentence.
In this day and age of crazy people, I try to be polite to all strangers, because I certainly don’t want to offend someone who may decide to retaliate. That may sound paranoid, but it would only be paranoid if I dwelt on it. When I force myself to be polite in situations where rudeness seems justified, I almost never make the decision based on fear. I don’t think that people may be crazy, only that I’ve decided to try to be polite. It’s like buckling seat belts. I almost never think in terms of potential accidents, just that I should buckle them. Unlike seat belts, routine politeness brings more immediate positive results than buckling seat belts. People tend to be nicer to me.