My Explanation (Cross-posted from Digg)
For those of you who don’t get it. A “Bel-Air” is a story that starts out talking about something else, and then at the end, shifts into the ending of the intro to the TV show “The Fresh Prince of Bel-Air”. It’s a prank.
In this case, a “Reverse Bel-Air” – you start by repeating the beginning of the intro to “The Fresh Prince of Bel-Air” and then, partway through, you shift, and talk about something else entirely (in this case, she’s breaking up with him).
Earlier in the comments, someone posted an analogous situation – would you like to see a video of Rick Astley singing “Never Gonna Give You Up”, but instead it goes to a different song. This would be a “Reverse Rick Roll”
You win at Digg!