It's an expression use to describe the harsh feelings of wanting to use the toilet really badly.
Is a game where two or more people try to hold out from craping in there pants the longest. The winner is the person who does not shit themselves.
You know how a turtle sticks his head in and out of its shell? Well that's what I'm doing to my ass, I'm playing turtle with my crap.
This is what happens to a man's penis and testicles when he gets scared, nervous or cold. His junk has major shrinkage.
I took my pants down to show her my big unit, I guess I was nervous and it was playing turtle on me.