Could be something moving backwards or maybe the return of someone/something.
"Yo, bro did you hear about rregretzz?"
"No what happened?"
"He is back!"
When someone stops at a red light next to an old person, slowly starts backing up, and yells "put on your brakes!" at them.
I can't wait for the day I get to back-up-break some unsuspecting old fart!
A person with a back that looks like you’ve been dragged along the road for days
Look over there Ernie it’s scabby back
Indicates that the person engages in sexual intercourse with the same sex
Dude, look at that guys fork in the back pocket, he likes men