Flywheel

A description applied to a girl with large breasts, a large butt, but who is otherwise thin and scrawny. The term comes from the fact that she is distributed weight-wise similar to a flywheel, implying that if she started to fall she would roll.

Man, you should've seen this girl: skinny but with a gorgeous rack a huge ass. She was a total flywheel.

Mexican flywheel

The Mexican Fly wheel is a dangerous sex position where a male Mexican suspends himself from a calling fan and flys around the room while the woman jumps on top backwards. This now becomes a flywheel as they are flying around the room

Hey do you want to try the Mexican Flywheel tonight ? I am feeling dangerous.

missing a flywheel

Adjective phrase:

A descriptor applied to a person who functions well but is "not quite right in the head," as indicated by small but noticeable eccentricites of behavior to which said person is oblivious.

"Sure, Jeff is great guy, but he leaves the impression that deep down dude's missing a flywheel."