n. someone who is constantly doing things in a very awkward and vociferous manner as they squeam and squirm around trying to make sure they are not left out of the party or whatever might be going on; usually a very annoying person; it comes from there being 8 available tits to suck on (a dog that has just mothered a litter of puppies), and the 9th puppy is the one making all the ruckus trying to find a place to suck with no teets available.
Ninth puppies (esp. males) that grow up and obtain power are often consumed with the Napoleon complex or little man's syndrome.
My kid brother is such a ninth puppy. He's always nosing into what me and my friends are doing and won't just shut up and go away.