Pauly D & Baby Mama -- The Boozy Vegas Hookup ... Caught on Camera

Hours before Pauly D knocked up Amanda Markert, they were both raging at a crazy pool party in Vegas ... and TMZ has several pics of the boozy scene right before the drunken conception.

The two met at the legendary Rehab pool party at the Hard Rock Hotel in the summer of 2012 ... Pauly was working the DJ booth and Amanda was partying her face off in a smokin' hot bikini.

At one point during the party, Amanda somehow got on stage (probably because she's hot) ... and sprayed down the crowd with a bottle of champagne. Later she was seen double-fisting novelty-sized cocktails.

Soon after that, she got some one-on-one time with Pauly -- and 9 months later she gave birth to his daughter. A true love story ...

But the connection they had in Vegas stayed in Vegas ... 'cause now Pauly and Amanda HATE each other's guts and are at war over custody and child support.

Vegas baby, VEGAS!!!