Jack Lemmon's OVERacting...
The Apartment is the first movie I have seen with Jack Lemmon.
Lemmon is clearly overacting throughout the whole movie (in almost every scene).
Maybe this was normal for the 60s, but seriously, the farce looks almost like a sitcom. I.e: "Bewitched" TV show from the 60-70s where the male character does the same overacting (as Lemmom in The Apartment), but appropriate for a TV show.
I guess Jerry Lewis was overacting in his movies as well in the same period, but his was a deliberate method that was part of his comedy routine, ditto for the way Woody Allen effectively overacted through the 70s and 80s.
But Jack Lemmon was trying (and desperately failing) to do both drama and comedy. It was as ridiculous as that awful Rodney Dangerfield OVERacting in that film Back to School, where you are supposed to first cry at directors cue and then to laugh and then to cry again.