The story
Compare typologically Russian хоть ссы в глаза́, всё бо́жья роса́ (xotʹ ssy v glazá, vsjo bóžʹja rosá).
Etymology from Wiktionary, CC BY-SA 4.0.
don't piss on my leg and tell me it's raining
Today it means: Don't tell me obvious lies. Full definition →