Bill Belichick Stuntin' In Greece, Hot Bikini GF and Super Bowl Swag

Look at Bill Belichick's face ... that's the MOST we've ever seen him smile -- and it's all because he's on a sick vacation with his beautiful girlfriend ... and still reppin' Boston, HARD!

Bill and Linda Holliday are vacationing off the coast of Greece -- where they're riding on yachts, playing on the beach and visiting some of the historic sites ... including Stadium at Olympia!

FYI, the stadium is said to be the oldest in the world -- and Linda commented, "Someone feels right at home!"

By the way, check out Bill's hat ... it says VII Rings ... the name of his boat back in the United States, which was named after all of the Super Bowl titles he's won.

The hat is clearly an older one because he changed it to "VIII Rings" after the latest Super Bowl win back in February.

Bill and Linda have been dating for years -- and some think it's just a matter of time before she gets a ring of her own!