The phrase 'your ass' or 'your arse' British Isles English is often used to simply refer to 'you'. There is a pun around "saving my ass" in Shreck I. Also "my ass is on the line, not yours" - "I am on the line. Imagine somebody saved him from this situation the man would embrace him " thank you bro! Is it an informal way of saying "Thanks for saving my life"?
I lied that you went shopping with me when in fact you were cheating on your wife, would be the more common use, or something similar.
Liliana, you're right - some women do use the this expression, but I still think it has a slightly masculine flavor. That doesn't mean that woman can't use it; it just means that, when they do, the usage lends their speech a somewhat tougher quality, which may be desirable for some women in some circumstances. Beryl from NorthallertonMar 15, You must log in or sign up to reply here. LilianaBMar 16, Also "my ass is on the line, not yours" - "I am on the line. It's simply a quite conventional use of the figure of speech "synecdoche," using a part to stand for the whole.