How do you get off on an electric toothbrush

By sticking it in your vajayjay.
How else?
The electric toothbrush is a cheapskates vibrator. You can brush your teeth with it, and get yourself off. It's a two for one

I feel like that's pretty self-explanatory. It vibrates and some of the bristles spin. All you really need is something that vibrates.

There's a school in my province (all girl school) that banned vibrating tooth brushes.