Nut or Butt

A phrase used to ask whether something is good or bad, with nut denoting good and butt denoting bad.

Crazy about behinds!

a situation where a group of people usually males are packed into a small space and end up extremely close together

Guys riding 2-up on a motorcycle; or more generally, riding any 2-person device where one individual sits directly behind the other (second person being a male).

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!

adjective: used in a very crowded or tight situation.

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.