The Mel Brooks Number

So you have a musical number. The music is absolutely beautiful, and hearing the instrumental part just makes you want to cry or go "Awwww...". But wait, something's wrong. There is something that is keeping you from bursting into tears. What could it be?

Humor.

You're hearing a Mel Brooks number, which is not necessarily a bad thing unless you're a drama person. This kind of song can be classified as one of the following:
 * A song with beautiful or classic-sounding orchestral arrangements but that features humorous, gay, or inappropriate lyrics.
 * A song with said orchestral arrangements and gorgeous lyrics, but the actors move in a humorous way while singing it, or they just look funny.
 * A song that sounds like the perfect Tear Jerker...unless you knew what it was really talking about.

This kind of song is always Played for Laughs. Named for the quintessential example, Mel Brooks, who became master of this trope after he started writing musicals.

Film

 * The Trope Namer is Mel Brooks. Many of the songs he writes fit this trope in one way or another, most obviously Springtime for Hitler.
 * A famous Brooks anecdote is that Frankie Laine didn't realize Blazing Saddles was a comedy when recording the theme, and Brooks didn't have the heart to tell him after such a sincere performance. Hilarity ensued.
 * Robin Hood: Men in Tights gave us a... rousing performance of "The Night is Young, and You're So Beautiful" with all the Merry Men sitting down to enjoy the show. At the end of the song it looks like Robin has a 3-foot erection (which prompts a standing ovation from his men followed by disappointed sighs when the optical illusion is broken and they realize it was just his sword).
 * In addition to Springtime for Hitler, the musical version of The Producers also gave us "Der Guten Tag Hop-Clop" played over the credits in typical Award Bait Song style.

Theater

 * "Something Has Happened", from the little-known musical I Do! I Do!
 * Chicago has "Class", which has a beautiful melody but is packed with swearing and grammatical errors.
 * The Book of Mormon is full of these.
 * While the entire show is hysterical, "You Won't Succeed On Broadway" from Spamalot is definitely one of these... especially since the song talks about Broadway shows flopping if they can't get Jews in the cast.

Western Animation

 * "Up There", from South Park: Bigger, Longer, and Uncut. One of the better "I Want" Songs...sung by Satan.