I tried posting a message but the dumb system lost it... Oh well...
It's not Chinese, it's Thai (they are both tonal so it may be easy to confuse them if you've never heard either language before, Thai actually has 5 tones) and it's comprised of two words... "Yet" means "To have sexual intercourse with" or (more often) just "f**k. "Meh" (it would actually be written "Maeh" in English) means "mother". So the phrase literally means something between "motherf**ker" and "f**k your mom". It is a swear phrase but culturally it's viewed as a somewhat old skool expression... It can also be comical in some situations as I've heard comedians use this phrase before. Hope this helps. :]