“Never Smile at a Crocodile” as written by Jack Lawrence and Frank Churchill.

Never smile at a crocodile
No, you can’t get friendly with a crocodile
Don’t be taken in by his welcome grin
He’s imagining how well you’d fit within his skin
Never smile at a crocodile
Never dip your hat and stop to talk awhile
Never run, walk away, say goodnight, not good-day
Clear the aisle but never smile at Mister Crocodile
You may very well be well bred
Lots of etiquette in your head
But there’s always some special case, time or place
To forget etiquette
For instance:
Never smile at a crocodile

Putting a smile on her face