Throttle Thumb

When your thumb gets sore from holding down the throttle on a quad.

(after a whole afternoon of riding on the quad)
"Damn, I got throttle thumb!"

Thumb Throttle

A sex move where you repeatedly poke your thumb in a girl's bunghole, The same way you would press the throttle to rev a four-wheeler.

My girl loves the thumb throttle when I'm doing her doggy style! VROOM VROOM!