The future Hall of Famer turned all the way up at the JEMAA, The NoMad Pool Party at the Park MGM over the weekend ... where Gronk decided to put a full SHOW on for the crowd.

Someone gave him a sax -- so he played it!

Someone told him to do push-ups -- so he did 'em.

Someone gave his brother a bottle of vodka -- so he slammed it onstage!

Rob's bikini model girlfriend, Camille Kostek, was also at the party -- and helped Gronk celebrate by handing him a beautifully-crafted retirement cake ... which Gronk later smashed to pieces.

Sources at the party tell us Gronk's group had a private VIP area stocked with champagne and Don Julio 1942 ... because ... well, it's awesome. That's why.

Congrats on retirement, Gronk -- and remember to drink water!