Specifically, an individual whose car moves approximately one tenth of the speed it should be moving at.
These people may be found pulling out in front of you for no goddamn reason and slamming on their brakes. Such an event may prompt outbursts of wtf
or "you flaming cuntwaffle."
When applied in general usage, the term can refer to any jerk
"(whistling to self while driving)...JESUS! What the FUCK! Goddamn.... goddamn pokey SLOWFUCK!"
"Yeah, that guy's such a ... he's such a pokey slowfuck."