Smb

an abbreviation for Scratching my balls is a common element of Internet slang. It was used historically on Facebook but is now widespread in other forms of computer-mediated communication It is one of many initialisms for expressing bodily reactions inspired by smh(shaking my head) or (scratching my head) or which ever you prefer

for example:

JOHN: wats up

Rich: nothing much

JOHN: you going to the party tonight?

Rich: uh SMB Probably not

JOHN: Lol smb