Literally, a human buzzkill, as Paraquat is used to kill Marijuana thus literally killing potential buzz.
The Dude: You thought that Bunny had been kidnapped and you were fucking glad man. You could use it as an excuse to make some money disappear. All you needed was a sap to in it on, and you'd just met me. You...you...human paraquat!
by Buck Turgidson May 07, 2007