Jim Barris is a character in Phillip K Dick's classic science fiction novel of drug abuse, A Scanner Darkly. He is an associate of the protagonist who is nominally his friend but actually his enemy.
To explain Jim Barris, we have to say a word about A Scanner Darkly, which is a near future science fiction story taking place in a Southern California that, except for one or two technological points, is not at all different from the world that Dick lived in during the 1970s. So A Scanner Darkly is not so much a science fiction novel as it is a Comedy of Manners (or lack thereof) of the drug culture. Not that I spend a lot of time in the drug culture, but I am familiar enough that I realize how spot on the description of the characters and situations are.
Jim Barris is a drug user, addicted to the fictional Substance D, but exhibiting the signs of amphetamine use. He is also, compared to those around him, slightly educated, and uses it to bully them with odd facts and arguments that sound believable but are shallow and ill-informed. He is also an obsessive tinkerer, being a tweaker in both senses of the word. His inventions and devices seem to be unworkable or fictional, he tries to build a silencer out of "aluminum foil and a piece of foam rubber", an endeavor that ends up to no good, as does his theory that benzocaine is really just another name for cocaine, something that "only certain gifted people know". Jim Barris is the dark version of the resourceful MacGuyver Stoner. He also only has a few plans that work, all of which involve destroying things. His biggest act of sabotage takes no more technical skill than using a screwdriver and tearing out some wires, something that is admittedly beyond the abilities of most of those around him. The biggest part of Dick's skill in portraying Barris is that we never can quite figure out whether Barris is lying, believes everything he says, or is so far gone in drugs and megalomania that there has ceased to be a difference. Since the theme of the book is people's inability to monitor their own sense of reality, Barris' skewed self-perception fits in well. Barris' major role in the plot, other than generally participating in the stupidity, is to report his friend, Bob Arctor to the police as a drug dealer. He is, in short, an evil and treacherous man.
Even more importantly to me is the fact that the portrayal is so correct, that I now have a mental term to refer to a certain sets of behaviors by. When I come across a drug user with an exaggerated sense of their own importance and abilities, I tag them down as a "Jim Barris" and know what to expect.