the act of vomiting into a girl's vagina before having sex with her. doing Acid Rain usually results in Hydrochloric Penis (burns on the penis from Hydrochloric acid, or better known as stomach acid).
Man, that Acid Rain last night was amazing, but now i have a bad case of hydrochloric penis
the act of expelling gas (farting), then urinating on them. Similar to real acid rain caused by rain passing through hazardous pollutants in the air (smog)