I guarantee it! 

A term meaning "I agree!", however used by old men and/or young men. Idealy, women could use it also, however that has yet to be seen. Mostly used when no guarantee is in sight or even possible.

"It's cold outside!" "I guarantee it!"

I guarantee it! by T-Bone February 11, 2004

I guarantee it 

George Zimmer's closing statement, especially after the successful use of his monolithic man meat.

Hi, I’m George Zimmer, founder and CEO of the men's wearhouse. While surreptitiously plunging my rosy-cheeked cyclopean ally into the anal cavity of a young migrant farm worker of indeterminate gender in the front row of a movie theater, the poor youth screamed for more than three minutes straight, finally coughing up a load of 100% pure Zimmer sauce and passing out. The other movie patrons, angry at the interruption of the adventures of sharkboy and lavagirl in 3-d, began pelting me with drinks, food, and phone numbers hastily written on napkins. Unfortunately, my outrageously dapper suit was ruined in the process. I nonchalantly pulled the unconscious youth off my enormous eyeball gouger and stripped nude. Then, with a bestial roar, I beat the entire audience to death--without leaving the front row. On my way out, in the custom of the Zimmer family, I gave them a burial at semen. I guarantee it.

I guarantee it by ms. anonymous September 10, 2008