I've got to say, one of my favorite Chinese vulgar exclamations has always been "Wo cao!" It's pronounced with two falling tones, so it sounds roughly like the American English "Fuck me!" Essentially, that's about what it means, although the "Wo" isn't actually "I" - in fact, I don't know what the "Wo" in "Wo cao" actually means.
What I like about this one is that whenever I use it around my Chinese friends, they often respond with "Ni cao shenme cao" - like, "What are you fucking?" To which I often respond, "Wo can ni ma ge bi!" (If you're not sure what that one means, you should read our article about Bī - one of the most common vulgar swear words in the Mandarin language.
So yeah - "Wo cao" - my favorite piece of Chinese profanity. You can use it anytime something bad happens, like you drop your phone or someone tries to charge you too much while bargaining.