Original slang (i.e., invented and used by a very small group) meaning vagina.
Originates from hilariously flawed voice-simulation algorithm (in which "vasheen" sounds like "vagina" and vice versa).
Man: "Ma'am, you're being very aggressive!"
Woman: No actually, I'm vassertive.
Man: What the hell is 'vassertive?'
Female: "It's assertive with a vagina."
Man runs away screaming because a woman used the word vagina.