When a person starts a posting on a message board, or forum, or Facebook, that others are able to comment on, that original posting and the comments on it are called a thread. A thread hijacking occurs when one or more individuals commenting on the original posting, go off topic, creating a separate conversation. This is rude, and bad internet etiquette. If people want to discuss a different topic, they should start their own thread.
Below is a thread, consisting of an original posting and comments on that original posting. They illustrate a thread hijacking.

original posting: I'm so excited that my cat has learned to use the toilet with City Kitty! The training seemed like it took forever, but it's so worth it to not have to deal with a litter box any more! Has anyone else done this?

comment 1: Ugh! I just started training my cat, but he can't seem to move beyond the orange stage. How'd you get through that?

comment 2: I'm training my dog at PetCo classes. She's very smart. She learns the commands faster than the other dogs.

comment 3: I'm training my dog in PetCo classes too. They have great trainers. They're patient with the dogs and the people.

Comments 2 and 3 are off topic and are hijacking this thread. The person who made comment 2 should have started their own thread. The person who made comment 3 is guilty of continuing the hijacking.
by anon4mail January 9, 2012
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Either out of humor, or following a particularly frustrating event in traffic (Cut off, green light sitting, etc.), a passenger takes it upon him/herself to engage the horn for you.
Passenger: "Sorry for the horn hijack bro, that guy just really got to me."
by Brush_juan April 29, 2010
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emotionally hijack:

- the act of deliberately and successfully changing a particular person's (or group's) mood
Ex.1
Jim: We were having a great time, everyone was laughing their asses off, and then Karen walked in.
Bob: Let me guess, Karen started with her nonsense, emotionally hijacked everyone and ruined the mood.

Ex.2
Jim: Man, I was having a bad day, and then Glenn came in for a chat.
Bob: Let me guess, Glenn emotionally hijacked you and you had a super day!

Ex.3
The people who profit from 'mood disorders' do not believe in the fact that emotionally hijacking occurs all the time.
by GlennyJ December 12, 2013
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When you start the shower in the morning to get it warm, but before you can get in, your significant other jumps in front of you.
This morning I started the shower to warm it up but my wife shower hijacked me
by diabolikal30 February 8, 2010
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The occurrence of 2 or more people saying the same exact phrase at the same time.

But, instead of one of the participants exclaiming, "Jinx!" another person may exclaim "Jinx Hijack!" and "Hijack" the jinx from the victims, thus making them speechless.
{10:10:10 p.m.} Jack: I sure am hungry.
{10:10:10 p.m.} Brad: I sure am hungry.
{10:10:11 p.m.} Cecil: Jinx Hijack!
by Bradley Giglio June 29, 2008
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Choosing a word because it evokes a specific emotion rather than because it is accurate.
After 9/11 the word "terrorism" became a much more emotional term for Americans than before, when it was equally deplorable yet much more theoretical in most people's minds (i.e. something that happens elsewhere). Consequently, politically active people engaged in vocabulary hijacking by applying the term "terrorist" to their opponent's activities (e.g. environmental "terrorists", government-sponsored "terrorists", anti-choice "terrorists").
by FigurinOutLife February 10, 2006
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When you go to a website (usually via Google) and upon finding nothing useful, it wont let you leave by either:

A) Making you outsmart the website by pressing the back button twice in quick succession.

B) Giving up and opening a new tab because the above was futile.
"Damn, I wanted to find a picture of that CD, but this useless website Tab Hijacked me!"
by Polarity10 August 19, 2009
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