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 good-night, not good-day
Clear the aisle never smile at Mister Crocodile

You may very well be well bred
Lots ot etiquette in your head

But there's always some special case, time or place
To forget etiquette

For example:
One must positively not ever wear
a pleased expression on his countenance
when confronted with that large lizard-like amphibious reptile
who has long jaws, armoured skin and webbed feet
and who is known as the crocodile.

one simply cannot cherish an amicably
or trustworthy relationship with the aforementioned species.

In addition: It is mandatory that one does not become irresistably
drawn into the heironeous belief that the latteral open extension
of his lips means you are entirely welcome.

It is much more reasonably to assume
he is contemplating how you would look in a lizard suit

His! Hehe.
Clear the aisle never smile at Mister Crocodile