Big Sean -- EVERYONE Knows About My Enormous Dong

Big Sean would be SHOCKED if you didn't know about the fleshy firehose he's lugging around between his legs ... 'cause according to the rapper, "everybody" is aware of his super-large gift.

Sean -- whose member was unleashed to the world when nude photos leaked to the Internet last year -- appeared on KMEL 106 in San Francisco this morning when the DJ asked about the elephant (trunk) in the room.

Sean replied, "Everybody knows I got a big d**k, no homo, pause that."

The DJ then asked if rappers like Kanye and Wiz Khalifa measured up to him ... but Sean wasn't willing to dish.