look up any word, like swag:
 
1.
One that posts the final response to a post on a newsgroup, composed of an initial post about a topic and all responses to it.
Johnny once again became the thread killer as no one had a response to his irrelevant, off topic comment, befoere it was archived
by someguy March 13, 2005
 
2.
A person who makes some kind of awkward comment on a status thread, which stops the thread dead in it's tracks.

Some of the reasons for the thread stopping on the thread killer's comment:

1. Other threaders don't know this person well, so take the comment in a negative light.

2. They remember her/him being a "weirdo" in school/former or current job, etc.

3. Other comments in the past by the thread killer were confusing and possibly: crude, inappropriate or might appear hurtful, due to the absence of a smilies or winkies.
Look at how long this badminton status thread was going, until Brian commented this:

The best strategy is to try to hit the shuttlecock straight into the opponent's naughty places.

He sure is a thread killer!
by iconoguy April 03, 2010
 
3.
1. Someone who makes the last post in a forum thread.

2. A mod who is known for killing threads when they get off topic.

3. A person in a forum that is notorious for getting threads locked by the mods.
1. Nobody knows how to respond to bashturn's brilliant stupidity, so he is often a thread killer.

2. JPKeates usually explains why a thread must end with a great last post. He is a very accomplished thread killer.

3. CJ and Dug are thread killers, six threads got locked today because of their off topic ramblings.
by oli fant June 21, 2008
 
4.
a biting wit seen on facebook that effectively kills the thread, regardless of topic. 45 comments might be flowing freely on a thread, and then this person comes in, and either through wit, political incorrectness or pure non sequitur, prohibits anyone else from posting to the thread, effectively 'killing it'
dude did you see that thread that john had on his page?

yeah it was great until that guy posted the cameltoe pic!

i know, what a threadkiller.
by jerry potter April 06, 2011
 
5.
One who posts in a very popular thread on a message board, and then kills it. It will stay 'dead' from 20 minutes to a week, then the thread is fucked, and has no chance of become a great thread again. Just like a pron star that had testy cancer.
new post made by 'FolksyChipmunk' at: 2:34 AM June 24, 2001

currant date and time: 7:58 PM April 23, 2006

therefor he is a 'thread killer'
by buttsecks October 29, 2006