useless as..., adj. — Green’s Dictionary of Slang

useless as... adj.

SE in slang uses

In phrases

...a one-legged man in an ass-kicking contest

(US) absolutely worthless.

2001

playdospad ‘Founders Message’ posting 30 Aug. on ‘mtvsundergrads’ at Yahoo! Groups 🌐 Well Im back, and yes, where is the undergrads? Well, I am as clueless as all of you. The MTV site is about as useless as a one legged man in an ass kicking contest.

...a pork chop at a Jewish wedding (also ...slice of bacon at a Jewish wedding)

see under pork chop at a Jewish wedding phr.

...a spare prick at a (lesbian) wedding

totally useless.

1986–7		Maledicta IX 195: This article and series devoted to sexual slang would be incomplete without some notice of catch phrases, both British and American: […] as useless as a spare prick at a lesbian wedding.
2003		McGill Reed Dict. of N.Z. Sl. 222: useless as a fart in a bottle/a glass door on a dunny/a gumdigger’s dog/a spare prick at a wedding/a submarine with screen doors/a tit on a hand/an arsehole on a broom/an ashtray on a pushbike/the bottom half of a mermaid Completely and utterly and totally useless or incompetent. ANZ.