ass in a sling, have one’s

Also, get one’s ass in a sling. Be (or get) in trouble, in a painfully awkward position, as in When the news about the slump in sales gets out he’ll have his ass in a sling. Probably originating in the American South, this idiom may refer to so vigorous a kick in the buttocks (for which ass is a rude synonym) that the injured person requires a sling of the kind used to support a broken arm. [Vulgar slang; c. 1930]