U

up for it - to be willing to have a good time. Also for a woman to be sexually available.

uphill / upstairs gardener - a male homosexual. The term is a reference to anal intercourse. I leave it to your imagination to work it out.

up the duff - to be pregnant, usually by mistake. A 'duff' is a pudding (usually plum), so to be up the duff is to have 'a bun in the oven'.