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."
by AmbiguityReaper January 22, 2016
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