Someone who not only makes you horny but makes you want to cum just thinking about them. Just the thought or sight of them makes you want to nut all over and/or inside them.
duante: Look pear-shaped bitches like brianna love, mya g and miya g, they be so cumbussable
kanye: ye gentles got a ass that would swallow up a g-strings and up top, two bee stings
Basically a "cumbasket" is a vagina. But it could also be an asshole or a mouth, depending on where the cum is deposited. Anyways, it's mainly used as another way to call someone a "pussy".
The process by which, through the ingestion of an unruly quantity of phosphorous, one's ejaculate spontaneously erupts into flames upon expulsion from the penis causing widespread fear and panic.
Dave and Marie were dating until Dave's spontaneous cumbustion all over Marie resulting in a sudden case of the funerals.