The characters in these scenes were trying to one up each other in different ways. For Nelson Eddy, it was to show is prowess by having two dates at the table, and for Macdonald, it was to show off that she could be as talented and peppy as the girls themselves, that’s why she mocks them, until she realizes it’s only because she can’t beat them.
From these clips, you can probably tell that male sexuality is rewarded while female sexuality is shunned. The man has to be victorious over the females, as if he is supposed to beat out temptation or something like that.