as useful as tits on a nun

vulgar slang Utterly ineffectual, worthless, or unnecessary. Primarily heard in Australia. This umbrella is stuck inside out, so it's about as useful as tits on a nun at the moment. I know next to nothing about computers, so I'd be about as useful as tits on a nun trying to figure out what's wrong with your laptop. Until the power comes back on, all those microwaveable meals we got are about as useful as tits on a nun.