From Jargon File (4.3.1, 29 Jun 2001) :
LART // Luser Attitude Readjustment Tool. 1. n. In the collective
mythos of scary devil monastery, this is an essential item in the
toolkit of every BOFH. The LART classic is a 2x4 or other large billet
of wood usable as a club, to be applied upside the head of spammers and
other people who cause sysadmins more grief than just naturally goes
with the job. Perennial debates rage on alt.sysadmin.recovery over what
constitutes the truly effective LART; knobkerries, semiautomatic
weapons, flamethrowers, and tactical nukes all have their partisans.
Compare clue-by-four. 2. v. To use a LART. Some would add "in malice",
but some sysadmins do prefer to gently lart their users as a first (and
sometimes final) warning. 3. interj. Calling for one's LART, much as a
surgeon might call "Scalpel!". 4. interj. [rare] Used in flames as a
rebuke. "LART! LART! LART!"