Artist Disillusionment: The band hates their fans. All of them. (Even the hot ones.) They also hate other people in the music industry. They even despise working on new albums. Offdensen has to keep forcing them to work so they meet release dates and don't slack off all the time.
Beam Me Up, Scotty!: Dethklok is not the sixth/seventh largest economy in the world, just above Belgium. In the first season, "[Dethklok is] now the twelfth largest economy in the world, having just surpassed Belgium", in the second season they are declared the seventh largest economy in the world, in the third season, "[Dethklok is] now the sixth largest economy in the world". It can be assumed that they have become the World's Top Economy by Season Four, since they send the entire planet's economy spiralling downwards after all the copies of their new album end up lost/destroyed.
Defictionalization: Brendon Small has done several live tours as Dethklok, not to mention released The Dethalbum, which has the honor of being the highest-charting Death Metal album in Billboard's history. There have since been two more Dethalbums and a fourth for The Doomstar Requiem.
The Dethklok Fountain has now also been defictionalized, for those of you with $40,000 to drop on Adult Swim merchandise.
Doing It for the Art: While recording his guitar parts for a new album, Skwisgaar hears a buzzing noise. It only happens while he stands on the ground, though. To avoid the buzzing, Skwisgaar skydives out of the Dethklok airship and records his guitar parts in mid-air. When Toki accidentally erases the only copy of Skwisgaar's track, guess what he has to do again...
Skwisgaar: It may be the most dangerous thing I'll ever do in my lifes.
Toki: Then whys you does it?
Skwisgaar: Because, I ams a tones chaser.
Executive Meddling: Season 3 was shockingly tame compared to the first season; this was due to the fact that Adult Swim ordered the carnage be toned down, since Superjail (which had a similarly bloody tone) had debuted and they wanted to avoid people comparing it to Metalocalypse as far as ripping off it's tone.
Fan Nickname: After Charles returns at the end of the third season premiere with his newly acquired hero scar, several fans dubbed this even more badass version of him "Scarles".
Old Shame: Pickles used to be the front man for hair metal band Snakes n' Barrels.
The Other Darrin: Tommy Blacha was unavailable for the Doomstar Requiem special, so Toki's singing was provided by Mike Keneally, with Brendon Small filling in for younger Toki. Murderface and Dr. Rockso also had their singing provided by Brendon Small.
The Pete Best: Magnus Hammersmith, Dethklok's original rhythm guitarist, was eventually kicked out of the band for being violent and abusive. Toki Wartooth now holds his place in the line-up.
Talking to Himself: Brendon Small, Tommy Blacha, Mark Hamill, Up to Eleven. Go ahead, check out Wikipedia. See how many characters these people voice, not including background characters. Regular voices are more than double the regular voice actors. The entire band and CFO are voiced by two people.