horse manure

[den4]

A little old lady answered a knock on the door one day, only to be
confronted by a well-dressed young man carrying a vacuum cleaner.

Good morning," said the young man. "If I could take a couple of minutes
of your time, I would like to demonstrate the very latest in
high-powered vacuum cleaners."

"Go away!" said the old lady. "I haven't got any money! I'M BROKE!!!"

And she proceeded to close the door. Quick as a flash, the young man
wedged his foot in the door and pushed it wide open. "Don't be too
hasty!" He said. "Not until you have at least seen my demonstration."
And with that, he emptied a bucket of horse manure onto her hallway
carpet.

"If this vacuum cleaner does not remove all traces of this horse manure
from your carpet, Madam, I will personally eat the remainder."

The old lady stepped back and said, "Well I hope you've got a damned
good appetite, because they cut off my electricity this morning."

 

[lexico]

...horse manure from your carpet, Madam, I will personally eat the remainder.

Den4, that is the filthiest one I've ver heard!