the act of vomiting into a girl's vagina before having sex with her. doing AcidRain usually results in Hydrochloric Penis (burns on the penis from Hydrochloric acid, or better known as stomach acid).
Man, that AcidRain last night was amazing, but now i have a bad case of hydrochloric penis
When you get a woman to stand over your head, legs spread, and she administers a douche to herself and the resulting after fluids rain down on your head.