Cheering and clapping at the end of a movie is an American trait. Being British, the protocol we are supposed to execute at the end of a film is to glumly file towards the exits.
If the film was particularly enjoyable, it may be considered acceptable to quietly remark on this fact to the person on either side, although this it typically best done using Facebook, Twitter, or other social media.
But the scenes of Friday night were quite unseemly, and rather let the side down.
(Yes, "The Muppets Movie" was really very funny in places. I rather enjoyed it. Indeed, it is now Jack Black's second-best movie, after only "School of Rock".)
#7: "Pathfinder: Tide of Honour", by Tito Leati