Lyrical Dissonance/Western Animation

In the very first Goodie Gremlin short, the gremlins sing their cheerful, happy anthem to mayhem, war, terror and chaos and the causing thereof.
South Park's Christmas Time in Hell is a joyous song with its lyrics actually matching the tune... but it's a song that sings about how the Damned get the day off from being horribly tortured.
In one episode of The Flintstones, Pebbles and Bam Bam are found singing what sounds like an upbeat, cheery song about how "Smilers never lose, and frowners never win." Do you know why frowners never win? Because THE DEVIL WILL GET YOU IF YOU FROWN.
The Ren and Stimpy Show has the Happy Happy Joy Joy Song. Although the song itself is a deliberately insipid -- though insanely catchy -- song about being happy, it's the increasingly insane rantings of Stinky Wizzleteats (the singer) between verses that bring some dissonance. "I told you I'd shoot, but you didn't believe me! Why didn't you believe me?!" (The reason is that most of these lines are quotes or paraphrases of Burl Ives characters, but of course the typical viewer -- especially kids -- can't be expected to catch the references.)
- "I'll teach your grandmother to suck eggs!"
One Arthur episode has Art Garfunkel act as a one-man Greek Chorus to the characters' actions and feelings. This includes a part where he sings a lively song about Buster being "a sad, sad bunny." Buster then broke the fourth wall and demanded Art Garfunkel sing a more melancholy version.
The song "The Nowhere King" from Centaurworld has the tune of a lullaby and the first 2 words seem like they would fit right in with a lullaby, but the song gets dark quick and ends with

You will bring joy to the Nowhere King
When he sees the light leaving your eyes