Robert Pattinson -- Grabbin' a Handful of Booty

Twihards, prepare to be extremely jealous of FKA Twigs ... Robert Pattinson is showing solid PDA with his new chick -- grabbing a heaping handful of her cheeks.

The famous couple went to lunch Friday in L.A. and Edward proudly squeezed his new moon.

Still doesn't excuse his new haircut ... but we're guessing Twigs likes the doo -- and it probably helps RPatz play grab ass with her more often.

Glass is half full.