1) A parting taunt rather than an insult. Used to exude dominance over lesser beings (I.e Police, Chavs and Junkies) Ideally used when escapeing in some sort of vehicle, the poorer quality of the vehicle to better.
Akin to "I'll get you next time He-Man"
2) Something to shout at a person falling off a cliff.
1) "C U LATER" (Says a man on a Penny Farthing escaping the police)