Rob Gronkowski Jacked and Flexing After Terrible Super Bowl Week

Most people would sit and sulk after losing the Super Bowl and then having your house burglarized -- but NOT GRONK!!!

The New England Patriots tight end is rebounding like a champ -- flexing his muscles on a boat in Miami ... while partying with one of the biggest nightclub owners on the planet!

The guy in the driver's seat is Dave Grutman -- who owns LIV Nightclub. Forbes has dubbed him the "King of Miami Nightlife."

He clearly helped cheer up Rob Gronkowski -- who launched into a back workout on the front of the boat.

Look at it this way ... he's still rich, he's still jacked and he's still got 2 Super Bowl rings.