Thunder Pump
To hump someone as hard as you possibly can.
Mate, I thunder pumped that girl all night long!
Thunder-pumping
The act of vigorous masturbation, but only when it is so violent that anyone who hears it, assumes they are hearing rumpy-pumpy.
Person 1: I was totally thunder-pumping to your mom's Facebook last night
Person 2: ....
Person 2: ....