n. A person who doesn't have the faintest idea what they're doing and who, more importantly, refuses to do anything about it.
1996
Conceived and maintained by a contract programmer in Redmond, Wash., it is occasionally cutesy (he has names for each of the PCs on his home-office LAN) but saves itself with sardonic advice on topics such as the best way to handle what the programmer calls 'lusers.' (He recommends having a small, concealed LART, or Luser Attitude Readjustment Tool, available at all times. His preferred LART is, of course, a sledgehammer.)
1990 (earliest)
Much of modern computer slang is a residue of the hackers' heyday of late 70s/early 80s Ivy League America. What was once almost a complete language has left an unnervingly rich vocabulary of insulting terms for almost anyone else who has contact with computers. Something badly designed is brain-damaged, someone using a machine badly is a lamer, a luser, a nerd, (in Britain an anorak or a trainspotter), as well as many other things too.
This word is a blend of loser and user. In hacker parlance, luser is often used as a synonym for user, as though a mere user is automatically a loser, as well.