'Drat' is one of many expletives, like 'darn' 'or 'heck', which are harmless replacements for more offensive swear words. 'Oh, drat!' is the sort of thing that a polite person might say in a moment of annoyance, when they break something, or realise that they have forgotten something, for example. No, it's not rude at all. Do I use it? No, I don't think I do. It's a little old-fashioned. But now that you've reminded about it, I might just start using it...

"Drat" is used as a child-friendly version of "damn" or "shit". People say it in place of a worse curse word usually when around little kids. It can also be used humorously, since not many people say "drat" often.

Usually it is "drats!" with an "s" at the end. It is not used very often, but is said when something goes wrong. Similar to "darn it" or "dang it". It is not rude, it is sort of an acceptable version of a swear word.