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1.
1. In a familiar/joking context:
A friend or loved one who's chosen to employ an overtly non-subtle or border-line uncomfortable approach to drawing attention to something by a imposition of an appearance &/or behavior.

2. In a non-familiar context regarding a stranger:
An intrusively unapologetic & spatially-invasive creeper of the non-humorous or non-familiar variety or one who gives creeps.

3. A creepy animal, often nocturnal (e.g. Snakes, Possums); Can also be used lovingly to describe a cute, sneaky animal (e.g. Cats, Small furry pets).
In response to being made aware of their presence:

"What's up Creeposaurus?!"

In observation of their behavior which denotes the term:
"Hey there Creeposaurus..."

In response to the action of being a Creeposaurus:
"Wow, thanks for the creeps you just gave me!"
by Grilled-Cheese November 13, 2012