I always heard it called 'Thread Hijacking'. Unless you are talking about me, then it's just 'cute'. ;)

A-hole?;)

Perpetracious!

In my grandfather's day, they called them a butt-in-ski.

Misunderthreadknapper

thats an AButtmunch

A misreader. Mistaken. Misunderstanding. This person needs correction not abuse.

The "Boy, is your face gonna be red when you figure out how silly you look" syndrome.

butt launcher?

I think that would be considered evesdropping. I'm not entirely sure. But if it is then everyboyd does it.

Just plain rude:-)

thread-jacker, ABuffoon, Bag-jacker, ass-troll....

The best that I can think of are the following: Quarrelsome- stresses an ill-natured readiness to fight without good cause Impetuous- marked by impulsive vehemence or passion. However, I don't think either of those words are specifically accurate for the situation you're asking about. Hmmm, misguided missile? :p

Jack-in-the-bag, LMAO.

Human.?

Hothead works for me, not very creative but certainly accurate. You know what they say about assuming after all.

Buttinski ... that is the word my mother used.

Laughable works for me :)

dickhead

Opportunity

I know you have seen this in my comment to Rollie's answer, Brand, it was something of an inside joke. But presented for ever 1 else's consideration; Bobo-Spanish term for an unintentional clown. Someone who thinks they are doing the right thing, or doing a thing correctly, and doing it enthusiastically, with a lack of self restaint and discretion, but instead is making a fool of themselves. Rollie informed me it also a Cajun term for booboo, an error. And it is a term for something that seems to be one thing but is not. All those meanings seem to fit this situation. See this discussion on bobo for more info. http://www.answerbag.com/q_view/666394 I tend to see the humor in such tirades, sometimes the bobo sees it too, sometimes not, instead launching into another self defensive tyrade. I have committed the same faux pas maseff, I certainly saw the humor. Some of mine, and those of others have, lead to actuall highjackings of the thread. Some of them humorous, some actually serious on the topic of the original bobo, sometimes a combination. I try to keep the humor good natured and sympathetic and not sarcastic, insulting, or biting. Since I see the humor heres an alternative term from Bugs Bunny, "What a 'maroon.'" Bugs is tryin' to insult someone, but makes an error himself. It is self effacing but most people get the meaning and the humor.. He also manages to turn 'nimrod' into an insult, but I don't think that applies here. My vote goes to bobo, but then i am a Legoistic maroon. And my rod is not nim, thank you very much.

ABitard.

The word is "troll."

Love-deprived asshole.

Big-Meanie-PAnts

Republican.

To put it simply, a _nuisance_, a _pest_, a _pain_ in the neck or somewhere lower.

Entertainment.

..."buttinsky"?

We made up a word for this at work.You've been...you've been.... SLIPNOTIZED!

Fart

Are you sure that they are misunderstanding the dialog or that they are purposely acting like they misunderstand in order to disrupt things? I would just call it a unique opinion.