Rob Gronkowski got some pretty sweet BEER REVENGE on WWE superstar Jinder Mahal Tuesday night ... throwing some sudsy goodness right in Jinder's face during "SmackDown Live."

Remember, Mahal is the guy who doused Gronk in beer during WrestleMania ... leading to the NFL star's violent 3-point stance takedown.

But Gronk wasn't finished with Mahal ... and last night, sat ringside in Boston as Jinder took on his BFF, Mojo Rawley.

Gronk's becoming a perfect fit for the WWE ... makes you wonder if he'll trade the shoulder pads for a Speedo when he retires from the NFL.