someone who is annoying, clingy, a loser, or just a turn-off in some way, shape or form. They could be someone who is obsessed with you, but you have no interest in them whatsoever. see stalker
the origin of this word is unknown, people just started saying it so I thought I'd put my definition.
"he's been following me everywhere, emailing me, calling my house all the time, he's such a hackoholic"