Showing off a new (or "new to you") vehicle by driving it around the block (neighborhood/park/lot) continuously. It is a shortened form of "grandstanding." Term is typically usually used in the Southeast by adults who grew up in the 80's.
Man, he been granding his semi-new BMW all afternoon.
The act of doing completely random, strange, and weird things in public
Laughing randomly out loud for no reason while walking alone in public -GRANDing