And if I'm wrong, and Americans are not vulgar, then why so many people liked the dirty joke?
English is one of the most spoken languages in the world and is the international lingua franca.
Literally, any person who speaks English can liked that joke.
Don't be so narrow minded!
A mind which makes sweeping cultural generalizations usually trashes much of which could be of great value. How many times do you need to feel like a side of beef or, if you prefer, a pork belly before you find another venue to evaluate?
@ I_hate_clowns. You dislike a feeble joke on a website, so your first instinct is to write "NationalityX are vulgar". You then try to justify this by claiming that everyone who liked the joke that you disliked are "nationalityX", and therefore "vulgar". Check your prejudices. You're clearly deeply racist.
More fun meanings aside, can this also mean "take off the coat/ski-pants/boots/gloves/scarf/hat"? In Russia in the winter, getting ready to come inside requires a lot of effort. Would it be appropriate to ask "Почему ты раздеваешься?" to a someone who is taking off their outer layers, or does it only mean a full undress?
Seriously, though: – There seems to be a fairly close match between Russian and German in the use of reflexives; both employ them in many situations where English would not (e.g. 'to feel' or 'to undress'). Having studied German to some extent, I think this will help me to recognise cases where Russian calls for a reflexive.
Same with Dutch. "to feel" is "zich voelen", "to undress" is "zich uitkleden". This sentence would be: "Waarom kleed je je uit?". It's also similar to the Greek 'medium' form, having the same usage as the Russian reflexive: applying to oneself, passive, certain verbs that only appear reflexive (medium tantum). It does make it slightly easier.
Not grammatically wrong, but probably unfitting because of a hint of surprise. "Why do you undress yourself?" sounds like the speaker might believe that the person getting undressed should have had the undressing done by someone else, perhaps a king with servants who would normally help him prepare for bed. "Why are you getting undressed?" sounds much more natural. In contrast, look at the sentence "My three-year-old dresses herself," which implies pride that the parent doesn't have to do the dressing any more. "Herself" places emphasis on who is doing the dressing. But "My eight-year-old is getting dressed": The child is putting on her own clothes, and she does so to the surprise of no one.