pissing rain
(Irish slang) term used to describe particularly heavy rain, similar to "raining cats and dogs".
It's pissing rain outside, you'll get drenched!
piss rain
A weather condition characterized by heavy, drenching (usually warm) fog or mist, but few actual raindrops falling from the sky. Tends to make people more miserable than a true rainshower would.
Can be used as a noun, adjective, or verb, e.g.: "April in Boston equals day after day of piss rain," "They said it was supposed to be stormy, but it's just piss rain out there," or "I wish it would just go ahead and storm if it's going to; if it keeps on fucking piss rain like this I'm going to shoot someone."
Raining Piss
Heavy acidic rain. Taste sweet.
Student: Can we go outside and play?
Teacher: Not now honey, it's raining piss outside.
Teacher: Not now honey, it's raining piss outside.