Last week, I had the opportunity to take a dance class with Sevyn Streeter herself and learn some new choreography to her latest single, “Shoulda Been There,” featuring her rapper boo B.O.B. Now, while I was under the impression the class would be full of a bunch of fans and just generally interested parties, apparently REAL PROFESSIONAL DANCERS were up in there, picking up the dance moves immediately and instinctively putting their own stank…