Extract from the movie biography of Porter, "De-Lovely" (2004).
Costello (Declan Patrick MacManus) heard Winkler was doing this movie and came to the director offering his services. Winkler's idea was to have contemporary singers in period getup do the numbers--Costello's father was a trumpet player and featured vocalist with the Joe Loss Orchestra, and Costello said he was just imitating his father in this scene.

This scene was originally a quiet one in the script, with Porter getting the Irving Berlin telegram while playing at the piano. Later it was decided to have a party in the background (there were enough scenes already with Porter quietly at the piano), then later decided to expand it more show one of the many costume balls Porter threw, then you need music for the scene--and "Let's Misbehave!" was the obvious choice.
Porter loved costume balls and guests didn't have to bring one, he provided the costumes! His wild parties and general misbehavior (he wrote about himself alot) got him booted out of Venice.
Stars Kevin Kline as Cole Porter, and Ashley Judd as wife Linda.
Directed by Irwin Winkler, written by Jay Cocks.
The old Cole Porter make-up on Kevin Kline took 5 hours to complete.
Let's Misbehave -- music and lyrics by Cole Porter
You could have a great career,
And you should;
Yes you should.
Only one thing stops you dear:
You're too good;
Way too good!
If you want a future, darlin',
Why don't you get a past?
'Cause that fateful moment's comin' at last.
We're all alone, no chaperone
Can get our number
The world's in slumber--let's misbehave!
There's something wild about you child
That's so contagious
Let's be outrageous--let's misbehave!
When Adam won Eve's hand
He wouldn't stand for teasin'.
He didn't care about those apples out of season.
They say that Spring means just one little thing to little lovebirds
We're not above birds--let's misbehave!
It's getting late and while I wait
My poor heart aches on
Why keep the breaks on? Let's misbehave!
I feel quite sure affaire d'amour
Would be attractive
While we're still active, let's misbehave!
You know my heart is true
And you say you for me care.
Somebody's sure to tell,
But what the heck do we care?
They say that bears have love affairs
And even camels
We're men and mammals--let's misbehave!