Lou Talman relates: >But she refused to give me credit when I gave proofs, which she admitted were correct, of theorems proved in our book, if my proof was different from the proof in the book---saying "The man who wrote the book is a mathematician, and he gave that proof for a reason. You aren't a mathematician, so you must use his proofs. When you're a mathematician, you can use whatever proofs you want to."
I had a professor in college, for abstract algebra, who insisted on coordinate laden proofs when covering vector spaces. Now I had already read the book by Halmos (Finite Dimensional Vector Spaces) and who would want to write out those long tedious things once one has been exposed to that? Unfortunately, our bargaining on this topic was made more difficult by a language barrier -- he spoke little English and I don't speak Chinese at all (though I have later learned to count in Chinese ;-).
He eventually allowed me to write my nice short proofs, but I don't believe he actually ever understood them. (And just to preempt the inevitable -- some will say I didn't either - ha ha!)