Stalker

[Tina]

It seems to be that the term stalker no longer means what it used to mean--the pathological ANONYMOUS follower and tab-keeper of another person or persons (A detective who has not been hired and has no real reason to follow someone). The old definition also would say that a stalker often has an imaginary connection with the stalkee.
HOWEVER, common usage of the term, along with the term creepy, has come to be used as a defense mechanism for anyone seeking justification for not being attracted socially or physically to someone else.
This term is nearly as overdiagnosed as ADHD is in children. Any women who think an undesirable man might be interested in her will almost always automatically label him a stalker.
Note: Far too many idiots think theyre more important than they really are. Real stalkers seek out beautiful, interesting, and often famous members of the attractive gender. 90 percent of the people who use the term couldnt get a real stalker to save their lives.

[Dave Paprocki]

a person obsessed with another to the point of insanity. I.E. following one everywhere, calling constantly, not following restraining orders, collecting their hair in shower drains

[Couch Potatoe]

Someone who:

1. Literally follows a persons every move, on Facebook or otherwise.
2. Is way too obsessed with someone to the point of being a [creeper].

[Britney]

Edward Cullen

[Hina Muqadas]

I did not know what a STALKER is until I become one. A stalker can sit in a car nearby a persons house for hours straight. A STALKER poisons the victims WLAN ARP table and sneaks into the persons Facebook account and takes notes about the persons friends and comments. A STALKER observes who visit the person and feel enormous jealousy towards them. The stalkers would make quite good private detectives.
Most notorious STALKERS build a shrine for their victim and plaster the victims photographs on the wall around the shrine. They are the REAL PSYCOPATHS. More mild cases just write definitions into URBANDICTIONARY.