Does anyone remember that Night Court ep. where the Devil shows up on Halloween, gets Dan to sell his soul, and spends the rest of the ep. taunting Dan with tales of his evil deeds? Yeah it was
Just a friend of Mac’s,
but the joke wouldn’t have worked if it all wasn’t true. Dan tho is more of an inveterate hedonist than evildoer I’ll grant.
Michelle Tanner. Pure evil.
By any chance were you the head of NBC’s publicity dept, circa 1997? I recall there being a Seinfeld commercial bragging about the evilness of Newman…
No, Racheal Green. Self-centered as a gyroscope, only wanted to keep Ross when there wasn’t a better man around, used Monica for support and shelter, ruined almost every life she touched.
I hated that woman so much, I had to stop watching the show. I hope she got better, or killed horribly.
It wasn’t that long ago that Stewie killed his own mother (albeit in simulation), was it?
Oh, come now! Dr. Zachary Smith, of course!
I am shocked that there has yet to be a mention of Patsy from “Absolutely Fabulous” - I don’t have a specific cite (tho I bet someone here can come up w a pretty good example), but I do know that she was one mean bitch.
Ralph Furley’s brother, Bart.
Phyllis from the Mary Tyler Moore show.
Karen, from Will & Grace, but God, I LOVE her!
Oh, that’s a good pick. And underneath the superficial attachment to her looks and money, she is really quite an intelligent businesswoman. But ruthless when she wants something. (or if she thinks something might possibly amuse her)
TAKE THAT BACK!!
Karen is too beautiful to be evil.
And the white mess jacket wasn’t *that *bad…
oh Sigmagirl, I’ve met the most wonderful woman!
Burns - yeah.
Kelso would not be top tier, simply because the writers occasionally let him do the right thing, dammit! There was one episode where he pulled strings to let a man with no insurance stay until his treatment was done, rather than sending him to County… and another one where he gave the slot in a research program to the rich guy rather than the poor guy… which sounds evil until he points out that the rich guy would make a big enough donation to allow continued funding of some outreach program.
Alas, there was no such closure. 
Climb upon my knee, Sonny Boy . . .
Also in the evil department, don’t forget:
Janitor (name unknown) - Scrubs
Mimi - The Drew Carey Show
Reese - Malcom in the Middle
Swiper - Dora the Explorer
Swiper isn’t evil. He’s just a kleptomaniac. When he isn’t swiping, Dora interacts with him on friendly basis.
…and if Dora the Explorer is a sitcom, I’m just not getting any of the jokes.
Swiper just pretends to occassionally get along with Dora, all part of his evilness 
I don’t think Janitor from Scrubs is really evil. He helps people out occasionally. He’s more like an agent of chaos, inclined to upset the natural order of things.
For sheer depraved indifference, Dr. Venture from the Venture Brothers ranks tops in the evil category. He keeps his sons sheltered and considers them loud, annoying tools instead of children. He disciplines them with passive-aggressive snarks, keeps them naive and socially awkward, and mocks them whenever they show fear or weakness. He also keeps cloned versions of them in storage in case they die, so he doesn’t have to waste his time being a protective parent. They’ve effectively lost 3 years of their lives to reboots.
It’s the part where she asks you a question and then waits for you to answer, staring . . . at . . . you . . . and possibly fidgeting a bit. That deliberate breaking of the fourth wall and the sudden amusing but awkward self-awareness that arises in the audience as a result . . . man, don’t you get it?!