I'd be up her like a rat up a drainpipe

simile

Means the speaker finds a woman very attractive, not a great way to hit on someone.

You'll also hear

Up like a rat up a drainpipealso means moving fast or eagerly

Something wrong or missing? Suggest a fix

Dry as a dead dingo's donga
Extremely thirsty. Also used for weather that has not seen rain in months.
Flog it like you're 15 again
Going at something with great enthusiasm. A masturbation joke.
Show us where the roo scratched you
Asking a woman to show you her genitals. Probably not the smoothest way to do it.
You're rooting this cat, I'm just holding the tail
It's your problem or project; I'm only helping. Don't blame me.
Off like mum's pants on Father's Day
Leaving right now, in a hurry.
He'd root a snake's mouth if someone held it open
He will have sex with anyone or anything.