I rewrite lyrics in my head all the time, probably because of my childhood reading Mad Magazine.
As a guy who hates the Yankees, I came up with this one day watching CC Sabathia:
Your pinstripes bend
like lines of longitude
how fat thou art
how fat thou art
Fellow parishioners probably wondered why the entire family was giggling when the original was sung at mass, with me contributing my own version.
There’s a warm wind blowin’ the stars around, and I’d really love to see you tonight.
Yep. ‘My sca-rotum!’ Also, ‘My bologna’ and ‘Smith-Corona’.
As I recall, it’s specifically FDR himself who changes it to “only.”
Source: I’ve played FDR onstage twice. 
As far as I’m concerned, Powderfinger by Neil Young begins with the line: “Look out mama, there’s a whitebread voodoo honky mufuh!”
There’s a lot that goes into that, but it’s now etched in stone. There’s many ingredients. One is Powderfinger by Neil Young, another is Susanah from the Dark Tower stories, another is a couple of my crazy friends, another is a good amount of the Mary Jane, making us all of the same loony mind, and another is a loud stereo. It was almost bound to turn out that way.
But that’s how it is for good now.
I might be the only one, but I always sing it this way
Steely Dan’s Reeling in the Years
Are you reelin’ in the years?
Stowin’ away the time
Are you gatherin’ up the cheese?
Have you had enough of wine
More of a phonetic misunderstanding, a homophonic confusion more than an outright change:
Steve Miller Band Fly Like an Eagle
Shoo the children with no shoes on their feet (as in, go ‘way children!, including making shooing motion with my hands)
How’s the people livin’ in the streets? (they’re fine, thanks for asking)
Original: Put your hand in the hand of the man who stilled the water.
Instead: Put your gland in the hand…
Original: I want to hold your hand.
Instead: I want to hold your ham.
When we were kids, girl often became squirrel. Imagine my joy when listening to Alvin and the Chipmunks
Original: Jessie’s got himself a girl and I want to make her mine.
Alvin: Jessie’s got himself a squirrel…
There was a thread not long about about swapping heart for fart.
ETA: @Robot_Arm beat me to it on girl/squirrel
And I forget the comedian’s name…I think he played a guitar that looked like a flamingo. Instead of “My Sharona” it was “Rice-A-Roni.”
I read these lyrics on this board years ago:
Feed the children
Who don’t have enough to eat
To the children
With no shoes on their feet
I often hear it as “Shoot the children”.
Heading off to Iscandar
Who knew that it was so far?
I shoulda brought a candy bar
I’m going to starve to death!
Since she put me down there’s been owls puking in my bed
I do the same with Come Dancing by The Kinks, where I replace “Come Dancing” with Ted Danson:
Ted Danson
All his girlfriends used to come and call
Why not Ted Danson?
It’s only natural
I’m totally stealing this ^ and imagining other substitutions (for correction, protection, selection…)
(Joni Mitchell) While driving through the country, past the guernseys etc.:
“I’ve looked at cows from both sides now…”
(Steve Miller)
Original: “Jungle love, it’s driving me mad, it’s making me crazy”
Revised: “Jungle love, it’s strawberry mad, it’s making me crazy”
(Spirit in the Sky)
Original: “Go to the place that’s the best”
Revised: “Colder the place, that’s the best”
(Paul Simon) : She get down her knees and hug me and she love me like a rock
(revised): She get down her knees and hug me…and she ugly like a rock (she ugly like the Rock of Ages, she ugly)
It doesn’t fit but…
We always called Barry Manilow “Barely Man Enough.”
This isn’t comical, just a weird preference.
Steve Martin and Edie Brickell have made three albums together. My favorite is their first, Love Has Come For You, and my favorite song is “When You Get to Asheville.” There’s a lyric:
She won’t sleep in the house now
She just listens for the sound
Of your old '84 Ford
Coming down the road
I just hate the sound of “Of your old '84 Ford.” It messes up the meter kind of unforgivably. When I sing it, it goes:
She won’t sleep in the house now
She only sleeps in the yard
Waiting for the sound of
Your '87 Ford.
I hate correcting lyrics, almost as much as I hate lyrics that need correcting.
I have a good friend who is quite hard of hearing, but he grew up in a very musical family. He has all kinds of wrong lyrics. I think my favorite is
“Pardon me, boy, is that the cat who chewed my new shoes?”
That’s Chattanooga Choo-choo if it’s not obvious.
I try to avoid the word ‘cute’, but that was.
Mentioned maybe a couple months ago that “glue” is usually an ok substitute for “you”.
Rod Stewart:
If ya want my body, and ya think I’m sexy,
Come on, honey, make it {{{grow}}}.
(last word said with heartfelt, lingering lasciviousness)
I’ve heard that one, but with “Pardon me Roy,” and it was the punch line of a joke about Roy Rogers, Dale Evans and a mountain lion hunting expedition.
Another Tom Petty song, “Rebels” - when he sings “I was born a rebel” I have to change it to “I was Barney Rubble”.
Use to always sing this to that Ozzy song: I’m going off the rails eating Gravy Train. (A reference to the dogfood.)