'MythBusters' Star Proposes to GF

"MythBusters" star Grant Imahara just busted another myth ... nerds do score hot chicks, and he put a ring on his to seal the deal.

Grant popped the question to his longtime GF, Jennifer Newman, Wednesday night at Clifton's Cafeteria in downtown L.A. Most of the 250 guests thought they were there for Jennifer's surprise bday party, until Grant got down on bended knee.

As for the ring, it's a vintage 1.56 carat sparkler Grant found at an antique dealer in San Francisco for around $20k.

No wonder her answer was "F*** yeah!"