A person who participates in forums, etc, online seemingly with the sole purpose of getting on people's nerves. Seems to have no clue at all, and will eventually be banned, kicked or otherwise ejected from the area.
A wannabe hacker that is just a script kiddie who goes around pwning everyone with his leet skillzzz.
Lamer: I has 0-day exploit! i r own peoplez now lulz
Hacker: Fucking script kiddie...
Lamer: stfu i r teh l33t
Hacker: *withdraws $1337 out of the lamers PayPal.*
Lamer: d00d wtf somebody just stole my monies!
(noun) An individual who is acting in a frustrating or annoying way. Someone who is not behaving appropriate to their current situation or is putting on a general disagreeable attitude.