Jamie McCarthy/Getty Images Jay Z made a rare onstage appearance at the star-studded opening night of Sean " Diddy" Combs ' Bad Boy Family Reunion concert Friday. Jay Z and fellow surprise guest Mary J. Blige performed their 1996 track "Can't Knock This Hustle." Jay Z also performed his 2003 hit "Public Service Announcement (Interlude)," which Diddy called his "favorite joint." On the track, Jay Z raps, "I got the hottest chick in the game, wearing my chain."