A statement made when one urgently needs to take a large dump. This is a visual reference referring to a piece of feces (the turtle) hanging out of the rectum, and "sniffing" one's underpants. This can also can be used to describe the moments prior to soiling yourself.
Brad: "Hey Alice, let's go have sex!"
Alice: "Hell no, after eating that egg salad the turtle is sniffing the cotton"
Carl: "Forget the roller coaster guys, the turtle is sniffing the cotton"
When a woman is giving a man oral sex and mid-way through his penis decides to roll back into his body and form a vagina. Then the woman proceeds to put on a strap-on penis and fucks him in the vagina. She stretches his penis from the inside and when it comes back out it is very red and fat. The man then choke fucks her in the mouth until he climaxes and when he does he pushes her head so far on his dick that cum shoots out of her nose and maybe her eye.
I was at my grandma's house and we were drinking tea while watching the news. I looked at her and said, "Hey Grandma." and she replied, "Yes?". "Do you want to do the flaming turtle?". She immediately bent over and sucked me off.