Ben Affleck -- What's Growing On with My Face? (PHOTO)

Ben Affleck is carefree when he goes back to his old stomping ground -- as in he don't care how long his beard gets or how disheveled his hair looks ... 'cause it's Bahston ya bastahds!

Ben was wicked scruffy and puffy as he walked around South Boston Wednesday scouting locations for his upcoming Prohibition era flick, "Live By Night." He's set to direct and star in the film.

We'll just assume (and hope) he's letting it grow for the role.

Or maybe Jennifer Garner just digs the look.