The two shortest for me in a jet have been:

(1) Luxembourg - Saarbrucken. A couple of times it looked as if the plane was slowing down. Probably they did not want to arrive too early or people would ask for a refund.

(2) Juneau - Gustavus (Glacier Bay). Alaska Air anounced it as the shortest in the world. Surely it isn't but it was pretty short.