1. Amazingly ugly, resembling a train wreck only worse. 2. To show severe annoyance. 3. I don't care. Example: 1. You look like a rat's ass this morning. What time did you get in last night? 2. Rat's ass. 3. Who gives a rat's ass?
RAT'S ASS
Meaning of RAT'S ASS in English
Slang English vocab. Английский сленговый словарь. 2012