When a girl has your load in her mouth, and before she can spit or swallow, you make her laugh which causes it to then erupt out of her nose.
Guy 1: Dude, this chick was giving me head last night, and she was going to try to spit it out, but instead I said something really funny and it came out of her nose and she fucking snowconed all over herself!
Guy 2: Nice one! That will teach that bitch to try and spit out the cream filling!
A variation on a snowball. When the girl who just finished blowing you attempts to "refund your deposit" you punch her in the nose, causing her to spit it out and bleed all over it, dying it red. Hence the snowball becomes a snowcone!
That bitch I've been ballin' tried to snowball me last night so I gave her a snowcone.