Personally, I would say that giving oral is always polite. It’s something that most people enjoy, and a really fun experience to share together.
Some people are not quite as into oral sex, but that’s something that can always be discussed with your partner. Communication, as always, is the key.
As a quick side note, some people are pretty expectant of receiving oral once they’ve given it, and while I’m not down with all that selfish behavior, I think it’s something to consider. If someone goes down on you, they’re probably going to want something in return. But, as far as it being polite, well, absolutely. Everyone loves an orgasm.
-teagan.