The massive diss went down in Miami's Club LIV on Sunday night. Weezy was onstage, next to the DJ booth when the drink was hurled from a VIP booth above ... where Birdman was standing.
You can't see it in the video, but sources inside the club tell TMZ ... Birdman did it. Also, we're told Wayne was doing his song, "CoCo -- which is basically a diss track against Birdman and Cash Money.
Seems crazy they'd show up in the same club -- considering their legal feud -- but both came out for a Jim Jones party.
Watch ... when the camera goes up to Birdman's booth, there's a guy with a look that says ... "What? Do something."
Wayne's crew didn't retaliate -- but it's clear. The gloves are off.