Self-cleaning oven, the whole bit.
Neurologically it lowers the firing threshold for dopaminergic neurons. In very broad terms, this means your brain on coke requires less stimulus in order to make you feel like you've done something good. So you're sort of chemically primed to think that everything you do, everything you say, is really fantastic and you should keep doing or saying it. But the effect will be relative to a baseline, so if you're already pretty pleased with yourself on a normal day without coke, a couple of lines will probably make you unbearable.I've always found coke just amplifies your existing personality, so if it turns someone into a total cunt, they were a cunt to begin with.