save someone's ass

save someone's ass

or

save someone's butt

mainly AMERICAN, INFORMAL, RUDE
If you save someone's ass or save their butt, you save them from a dangerous or unpleasant situation. Howard rushed up to me and said, `Thank you, thank you, you saved my ass.' You should be grateful — I saved your butt! Note: You can also say that you save your own ass, meaning that you escape from a dangerous or unpleasant situation. She climbed out the back of the car to get away, to save her own ass.
See also: ass, save