Wow -- I've just spent 20 minutes reading this one thread! This is a good one!
Mine, and I hear it VERY often: "SPAYDED" (I'm not even sure how to spell that!).
As in, "Yes, Doc, she was spayded as a pup and got her shots".

Oh, and "Pancreatis" instead of "Pancreatitis".

This is medical snobbery, I know. But these two are really common and I have to suppress the giggles when I hear them.

On a non-medical note, if I hear "Get-R-Done" one more time.....!