Kim Possible's Rogues Gallery not only self-identify as evil without exception (there are no Well Intentioned Extremists in this world), but most try very hard to prove it. Shego, in particular, is a good example. She's clearly in it as Drakken's Dragon for the money, but also tries to beef up her evil credibility on her own time; maybe because she used to be a superhero. One time, she was even manipulated into helping Kim Possible herself, when the heroine threatened to tell the world that Shego used to be a good guy.
Evil is a whole lifestyle in Kim Possible, with its own magazines (Shego reads Villainess while not listening to Drakken's Evil Plans), supervillain conventions and trade shows, and a corporation that supplies equipment and henchmen ("HenchCo"). Though a Disney-produced show, they aren't above take potshots at the corporate lifestyle and how nicely it dovetails with being a villain.
It even has an own TV show: Evil Eye for the Bad Guy.
The villain culture has a whole set of traditions, to which the bad guys generally adhere, even when they clearly give the heroes a chance to escape or turn the tables.
Several in Teen Titans. Early on, the writers couldn't even come up with a goal for main villain Slade. Few villains even got origin stories, so most seemed to just be causing havoc for the fun of it. Trigon was a card carrying member of this trope, but that's understandable, given that he's an eight-story tall red demon.
Slade's not as much of one as some - he never self-identifies as evil, and his plans are clearly building towards something (though neither the audience nor the heroes ever get clued in as to what that is). Better examples are Brother Blood, who teaches a supervillain school that includes courses on doomsday threats and "Theory of Mayhem", and the Brain, who actually puts the word "evil" in his organization's name!
Possibly the funniest example of this is Control Freak: A fat Expy of an overly-obsessed fan-boy who's only motivation is being seen as the Titan's nemesis by the Titans themselves! He's rarely a threat because of this, but because of his reality-warping powers he'd probably be their most dangerous foe if he just got serious and had a firm goal in mind rather than just getting the Titan's attention.
Same thing goes for the villains in El Tigre: The Adventures of Manny Rivera. They even have a villain quarterly magazine.
While, contrary to popular belief, Captain Planet's villains generally did have some kind of discernible motive (usually raw profit at the cost of the environment), causing damage to the planet for its own sake sometimes seemed to take a life of its own and supersede anything else. In particular, villains such as Verminous Skumm, Dr. Blight on a bad day, and the evil spirit Zarm tended toward the "Corruption/Destruction for its own sake" end of the scale since they were just completely evil and insane.
Azula from Avatar: The Last Airbender embraces the rest of the world's view that she's evil. She even calls herself a monster in the later episodes, but that's actually her way of coping with the self-loathing brought on by those beliefs.
In Dreamwave's comic book series, Starscream responds to a question as to their appointed task with "Who cares? With Megatron, you know it's going to be evil...and evil is always fun!"
Beast Wars' Blackarachnia spends a lot of her first season or so repeatedly telling the heroes that she's evil, bad, evil, not to be trusted, and evil, occasionally even resorting to actual action to get her point across to particularly irritating non-believers.
Silverbolt: Blackarachnia, I want you to return with me, to the Maximals. Blackarachnia: Get a clue, you canine cretin! I'm a Predacon! I'm evil! I'll shoot you— Silverbolt: No. My heart tell me that you will not. Blackarachnia: Oh yeah? * shoots him in the leg* Silverbolt: * shocked* You...SHOT me! Blackarachnia: No duh, Dog-Boy! I'm evil!! Now do you believe me? Silverbolt: And yet...you ensured the wound would not be mortal. Your inner Maximal goodness— Blackarachnia: SHUT UP, SHUT UP, SHUT UUUUUUUUPPP!!!
You can't say evil in that show without mentioning Tarantulas, whose outright villainy and treacherous attitude was something Megatron considered to be a viable asset.
In Beast Machines, Thrust and Jetstorm take on this role, while Megatron ironically believes he is doing good:
Thrust: Nothin' noble 'bout us, boy! Jetstorm: But savage? That we can do!
Aku, the Big Bad of Samurai Jack, identifies himself as "Master of Masters, The Deliverer of Darkness, and the Shogun of Sorrow." His name even means evil in Japanese.
The Venture Bros.: Every SINGLE villain in the series is a card-carrying villain belonging to the aptly-named Guild of Calamitous Intent.
Which, ironically, is depicted as having an important honor code and being an accepted facet of society.
Xiaolin Showdown has both examples of this: most of the Big Bad are Black Cloaks and Jack Spicer desperately wants to join their club and get respect. One Big Bad comments that Jack tries so hard to be Evil because of his insecurities.
Jack refers to himself several times as an "Evil Boy Genius". He also has club jackets with his face and "evil" on it and, of course, he has an evil trademark laugh.
He didn't just trademark his laugh, he stated he was adding evil and other such words to his devices to "create a brand".
The Powerpuff Girls is full of these guys. Mojo Jojo is the most notable. Subverted when he actually manages to take over the world, and turns out to be a benevolent ruler who makes the world a much nicer place to live. Double subverted when he quickly realizes that Victory Is Boring, so he gives up his power and returns to causing mayhem purely for the fun of it.
The Sonic Sat AM version of him as well, though to a lesser extent...his "pretend to be good when it's practical" moments are a bit longer and more pronounced. However, he's inclined to boast about his evilness as though it was something to be proud of, especially when in the company of those he believes are evil.
Robotnik: I want the location of Lazar's lair. Name your prize.
Lazar's guardian: You intend harm to my master.
Robotnik: Oh, you wound me dear guardian! I merely want to wake the grand wizard and honour his evilness! We have much in common.
Lazar's guardian: ...yes. I can see that.
King Koopa, Bowser's animated counterpart in all three of the animated Super Mario series, plus his seven Koopalings in the latter two series.
Really, just about every villain in the Super Mario cartoons counts as this. A prominent example: Wizenheimer in the Super Mario World episode "Ghosts 'R' Us." When asked why he does what he does, his answer is:
"Because I'm an evil Koopa Wizard! I don't need a reason to be mean and nasty. It's my nature!"
Other villains in the series tend to also be quite open with the fact that they're evil, there's even a company making devices just for super villains and a special driving test for them. Heck, they even have their own evil version of Santa Claus who rewards them for being evil!
General (under possession from the spirits): How would one contact this "Just-Us League?" Sergeant: I don't know, sir. Wear a gaudy costume and threaten a bunch of people? General: Thank you Sergeant, you've been quite a help.
Lampshaded yet again in Unlimited by Flash, during his Freaky Friday switch with Lex Luthor:
"Luthor": *Walking out of the bathroom* What? Polaris: You gonna wash your hands? "Luthor": No...cause I'm EVIL.
A bit of a plot point in the Legion of Super Heroes episode "Phantoms". Phantom Zone escapee Drax hears the voices of his still-imprisoned parents in his head, constantly reminding him that he's evil and always will be. Supervillains really do make Abusive Parents.
In the series finale, despite never having self-identified as evil before (quite the opposite, in fact), the still-alive villain says to...no one in particular, "Evil does not die. It evolves," in an ill-fated Sequel Hook.
In Rocky and Bullwinkle, Boris Badenov and Natasha Fatale are this trope, as is their nation of Pottsylvania. When Boris swears, he uses words like 'decency', 'honor', and 'joy'. He is occasionally awarded the "Order of the Double-Cross" by Fearless Leader, and when Natasha calls him a "sneaky, fiendish, rotten, no-good snake in the grass", she means it as a compliment. For a taste of Pottsylvanian culture, listen to their National Anthem;
"Hail, Pottsylvania, Hail to the Black and Blue! Hail, Pottsylvania, sneaky and fiendish through and through! Down with the good guys, up with the boss, Under the sign of the Triple-Cross! Hail Pottsylvania, Hail, Hail, Hail!"
In the movie, when Natasha starts musing about what a wonderful life they could have together if they could only stop moose and squirrel, she mentions about how they could have children that they raise to be "little monsters". This is mentioned in the same breath as them living a peaceful life in a house by the sea.
In Code Name Kids Next Door, villains eventually evolve into this, having 'supervillain meetings' and a supermarket for villains only. This even goes so far as a 'Villain's Choice Award'...on public television!
On a character basis, Father calls himself the second most evil adult, then refering to his father as the 'World's Most Ultimate Evil' before reawakening him. Grandfather goes on to refer to himself as pure evil.
In the episode "The Temple of Juatchadoon," Isabella parodies this. When accused of being a dirty double crosser, she produces yet another card from inside her outfit. "Isabella Garcia-Shapiro, Dirty Double-Crosser."
Dick Dastardly is a true, if ineffective, card-carrying villain, and probably the most popular bad guy in the Hanna-Barbera stable. The narrator of Dastardly and Muttley in Their Flying Machines calls him "the deadly, diabolical, despicable demon of the skyways."
Same for the original. The Lunataks are almost as bad.
A number of Danny Phantom villains refer to themselves as such (most notably Technus). Big Bad Vlad Plasmius initially averted this - for the first two seasons, being called a villain was almost a Berserk Button for him - but after Villain Decay began to set in he started acting more like a conventional card-carrying baddie.
Ren and Stimpy had a "professional bully," Victor, who showed Stimpy his Bully Union membership card.
Averted for The Light in Young Justice, the only time they ever do stuff like this is using it as a distraction to their real plan. They also have a benign name instead of the Legion of Doom or the Secret Society of Super Villains.