Hussing one off

Masturbating in a fast and noisy fashion while grunting frequently.

James: Lucas, you have been in the bathroom for 2 hours! Why are you grunting so loud?

Lucas: I'm hussing one off! AAAHHHHHH *Splooges everywhere*

sly one off

Having a cheeky wank without anyone knowing.

Be right back I'm off to sly one off before my wife gets back

Harry One Off

To potter - to do random aimless tasks and generally avoid doing stuff you should be doing. Procrastination.

Chippie had a hell of a lot of stuff to do but when I got home I discovered he had decided to harry one off all day and had done fuck all of any importance.