I definitely think it reflects badly upon a professional (any professional) if they consistently mispronounce words. It's irritating to people, number one, so they get a fingernails on the blackboard type feeling, regardless if that is an appropriate response or not. Secondly, it just comes across as sloppy - if you can't pronounce the word, it's understandable that someone may wonder if you "get" the concept.
I have a patient occasionally who always asks for her "Finnigrin and Dilauntin". It makes me clench my teeth, no matter how much I tell myself she is uneducated, etc etc. It's just irritating. I wish I could politely tell her that she's mispronouncing them, but that would result in a lower Press-Gainey score. LMAO.