A malaphor is the unintentional blending of different phrases or metaphors, such as "It's not rocket surgery" or "He smokes like a fish" I'd love to see some that you have actually seen, read or (better yet) used. My favorites are;
That's the way the cookie bounces. (I use that one regularly, just to see if people will notice.)
Take a flying hike.

What are some of your (clean) favorites?

He was three sheets to the mattress.
You're the apple of my pie.
It's raining cats and mice.
You don't have a floor to stand on.
That idea is really off the ceiling.
That's music to my speakers!

But what if the fish is salmon?

You can't put the toothpaste back in the horse.

"That's a horse of a different sexual orientation."

putting out fires with vaseline
for bitter or worse, in sickness and in hell
having a sneezure
deceased & desisted
odor of a lonely heart

High their, @djavous, finally decided to post did you?
Welcome to TSD.

Mine is one that's already been mentioned here (sort of):

That's a horse of a different kettle of fish.

To add salt to injury.

We got together to barnstorm ideas.

-Always drink upstream from the herd!
-They are like two peas in a pod.

dead as a cucumber

Ya gotta smash a couple skulls to make an omelet.

One of my dad's favorites: "If he/she had the brains that God gave broccoli...."

Not the sharpest knife in the chandelier.

But, possibly the most shocking one.

Stick that in your pipe and take it to the bank.

These Malaphors..are they a threat to Earth?..

(the poor cuke).