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5.
A threesome involving two men and a woman and double penetration. The two men configure themselves in such away that one man's nuts touches the other man's butts. Some say it's a myth and cannot be done, and maybe that's a good thing.
"Yeah man, Ray and Nick went nuts to butts on that broad all night"
by Joey Joe September 22, 2006
 
1.
adjective: used in a very crowded or tight situation.
hey, you dont wanna get in on that one (subway car), it's nuts to butts.
by mythodius November 08, 2004
 
2.
Although the above definition is correct, there is another situation it applies:
Nuts to Butts refers to 2 males riding together on a motorcycle or scooter - often times because the passenger is too lazy to walk to class so he hitches a ride on his buddy's scooter. Guys 2-up on a crotch rocket is the WORST way!
Looks at those 2 dorks riding nuts to butts to class.

Guy Passenger: "dude I need to save gas money, can you take me on your bike to the store?"
Rider: "nuts to butts? hell no"
by BMW Guy September 06, 2006
 
3.
A formation of military recruits that lines the nude men up in a single-file line such that one man's genitals are essentially pressing against the butt crack of the guy in front of him. This is done during induction between the time the men surrender their civilian clothes and when they are finally issued their military uniforms, to allow the medical examinations and inspections to be expedited.

The Nuts to Butts line up also has the effect of revealing those recruits who enjoy the experience as they would likely sprout an erection and could be rejected by the commanding officers who wanted to weed out homosexuals.
Recruits! I want you to line up nuts to butts and march into the examination room, NOW! MOVE IT!
by Fallo Turgidson October 20, 2013
 
4.
Also known as grinding, a type of club dancing where the male dry humps the female. Hence, nuts are to butts.
My high school banned nuts to butts dancing, but we can do it in college.
by Steven L Smith October 14, 2006