Literally - The bag of balls thats hangs beneath the penis/cock/dick/nob as part of the male genitalia.

Metaphorically - Someone who you really dislike and want to insult. It usually just comes out as you cannot think of a better insult.

the whale tail is the shape formed when a g-string rides up high over a womans trousers

Multi-purpose term to be used in any number of circumstances. Less harsh than dickhead. A variation on nobhead. Means scrotal sack, or scrotum, but sounds much better and gets quite addictive.

Condom (For those in Essex, UK. It's a form of contraception)

Tom Duncan. Au treasurer at York University 2003.

a person who is not being very sensible .

A nob sack is an insult and people can find it very offensive because then dont have a nob