Georgette singing on the Mary Tyler Moore Show.
Edith singing the somg she wrote on All in the Family
To me, it is the fact that the 'women" speak perfect english but cant parse the word “brain”.
But of course opinions differ-
https://www.quora.com/What-is-the-worst-episode-of-Star-Trek-TOS
This might be a good idea for a new thread.
F-Troop’s ripoff of the Gilligan’s Island episode. Instead of “The Mosquitoes,” the rock group with which they were competing was called “The Bedbugs.”
Does Bette Midler singing the theme to “Rochelle, Rochelle” count?
I love this episode! 
That’s the one, @ThelmaLou. Great detective work!
Now I’m thinking I may have to dig my DVDs out and watch that episode again.
There were several musical performances over the run of Scrubs - wish I could remember specifics. Some were really good.
Plato’s Stepchildren has the character of Alexander who makes a moral choice.
The Empath has Spock, Kirk and Bones exhibiting the strength of their relationship. Spock’s Brain has nothing
The Bedbugs included Lowell George and Richie Hayward, who went on to form Little Feat.
They’re still boring. 
The Internet Movie Database. You will find everything about every movie and TV show.
Yes, I had a “D’oh!” moment a few minutes after I posted that.
Never mind; I did dig out my Season 3 DVDs, and plan to watch that episode a little later tonight.
How I Met Your Mother had so much music that it almost doesn’t count as “usually non-musical” but the biggest and best moment was about suits.
So many good ones! Caught the first episodes of the reboot and they hit that “familiar but uncanny because they’re older but the same" vibe. I’ll still probably watch the series when I remember it’s on.
The one that sticks with me and wrecked me at the time and still makes me emotional, was one song in the “musical” episode where all the singing was revealed to be the symptom of a patient with a brain injury (tumor? Aneurysm? I don’t recall offhand). But the song though….
(From memory)
*It’s going to be okay. That’s what’s going to happen. Everything’s okay. We’re right here beside you, we won’t let you skip away. Live for tomorrow, ‘cause we swear to you, it’s going to be ok….
(We hope)”
And, now I’m crying. Fantastic episode.
That just happened to the episode I watched last night. (I had planned on finishing the season).
After Resident Alien, I watched an episode of Newsradio. They performed at a talent show. Vicki Lewis (a professional singer) and Dan Hartman (not a professional singer) sang Makin’ Whoopee.
The ‘Stop the Planet of the Apes, I want to get off’ musical in The Simpsons, featuring Troy McClure as astronaut Taylor. So many fine moments.
Ok, so, not a perfect example because short little *ditties are not uncommon in Bob’s Burgers, but this really stands out:
*A bit anemic without the orchestra, you might say.
The Magicians - The cast breaks out “Under Pressure” to rescue one of their own.
(had to link bc DC wouldn’t let me embed)