Ben Affleck Drives Jennifer Lopez Around St. Barts in Mini Moke Jeep

Ben Affleck is playing chauffeur for the missus on their tropical end-of-year vacay -- driving Jennifer Lopez around in a teeny tiny vehicle that he definitely looks too big to be in.

Hubby was behind the wheel Friday in a Mini Moke -- which is basically a toy Jeep for adults -- while cruising around St. Barts with his wife riding passenger ... and like we said, BA seems to be a bit crammed in there, even though Jen's enjoying the ride.

They were out enjoying the day in the capital of Gustavia ... where we're told they hit up Arawak Cafe for a bite, and later did some shopping at Jacques Zolty (a perfume store) and Bulgari (a jewelry shop) while perusing the town.

Of course, they were shoulder to shoulder for their stroll -- with Ben wrapping Jen up tight.

Earlier in the week, J Lo was spotted out on the beach in a bikini -- where her toned body was on display. No sign of Ben there -- but the dude was front and center in the streets.