First time I saw this episode had no idea what that scene was about.
Cliff Clavin, Norm Peterson, Dr Fraiser Crane.
Most of the old stuff im watching now (Cheers 8th Season Netflix) the simpsons referenced ages ago in their Goat period.
If I remember right they got all the voices for Cheers members for that scene except Kelsey Grammar as Frasier, who was busy but is a regularish Simpsons cast member as Sideshow Bob.