From Wiktionary, the free dictionary
Literally, “I shit on the bitch/whore/prostitute”.
me cago en la puta
- (vulgar, Spain, idiomatic) fuck; fuck it
- Synonym: me cago en la leche
- Used to express anger, irritation, contempt, or disappointment, but also to express happiness, e.g.: when meeting someone after a long period of time.