A phrase derived from the older phrase "Keep it on the DL". It was discovered in 2009 by scientist Ted Davis after a T9 error suggested flugelhorn instead of DL.
Ted: Hey, I think I caused Jon and Krysta to break up. But keep that on the DL.
Jack: Keep it on the Flugelhorn? OK, My lips are sealed.
Jack: Keep it on the Flugelhorn? OK, My lips are sealed.
by Touch the Sky December 13, 2009