Reactor is someone who rather than initiate conversation will just react to things said to them, often using one of their set repertoir of one liners. This earns them respect from over hearing third parties and creates the illusion that they are contributing witty banter. This often leaves the initiator looking like the boring person with no way to respond. In reality they are riding the initiator's creativity and steeling the glory. They do not feel social awkwardness and are happy to sit there without engaging or starting conversation. The initiator is forced to keep throwing topics into the mix, each one battered down with one liners leaving the initiator exhausted, bemused and scraping the barrel for conversation while the reactor seems oblivious to their crimes. They have nothing to give and are the scum of society.
Kanye West (see him being a reactor on the Sunday Night Project)
by Adagoof July 15, 2009
A person who often responds or behaves in a particular way in response to something.
Johnny comments on everything I post on social media, he's such a reactor.
by Misheard Metal April 7, 2016
Juno Reactor is a trance/goa electronica group. Started in 1990 by Ben Watkins and Stephen Holweck. Notable albums include 'Bible of Dreams', 'Shango', and "Labyrinth". They are best known in pop culture for their work in the Matrix movies.
Matt: My favorite Juno Reactor song is 'God is God'.
Chase: I agree!
by Erik N. February 4, 2006
Shotgunning a beer as an associate pours whiskey -- dammit, any hard liquor -- into the can.

D'you hear 'bout the fella that passed away?
Aye. Demolished three nuclear reactors in one sitting.
Limit yourself to one nuclear reactor per evening.
by edwinmassix May 9, 2011
A mixture of Cocaine, MDMA, Meth and pop rocks/
Kyle: Yo man, wanna go get fucked up?
Marco: I don't know man, only if it's a Chernobyl Reactor.
Kyle: Oh fuck yea!
by MaskedOliveMan October 17, 2019
A small, circle-shaped device that keeps the shrapnel out of Tony Stark's (AKA Ironman) heart. It also powers his kickass suit.
He's also got one back home that used to power his factory, until he used it to blow his insane business partner, Obadiah Stane, to kingdom come.
James: Did you see that arc reactor, man?

Gary: The glowy thing in his chest?

James: Yeah!

Gary: Yeah, I want me one of those, man.
by The Deegemeister May 22, 2008
A person who responds or behaves in the most aggressive possible way in response to something.
I said something controversial on social media and was berated for hours by nuclear reactors
by Misheard Metal April 7, 2016