It is a phrase that was used by video rental employees after handing customers their video tape.
The
act of rewinding a video tape after watching it is considered a kind deed, as the next
person to watch that tape wont have to rewind the entire
movie, which might spoil the storyline for them if they watched the screen while it rewinded.
Video
guy: "Here is your tape bro! Be kind rewind."
Customer: "Thanks man. I'll make sure my
parents aren't home when I'm watching it."