And what famous musician trying out his acting chops uttered the line "May I rub your ball, sir?"

I agree Babs is usually dire. But Judy Garland, IMO, was a far better musician/actor than Frank Sinatra on both counts.

And her daughter Liza was stunningly good in "Cabaret", and a few other films.

Harry Connick Jr is also quite good as a comedic actor. Perhaps it's a timing thing. As is Bernadette Peters, though whether she started out as a musical theatre person, I'm not sure. Goodness knows there are plenty of excellent musical theatre actors who sing well, like Kristin Chenoweth, who has been in a lot of good & awful stuff (she is a trained opera singer, I believe). She's even got the distinction of having won a Razzie! I love her.