You know what PhD stands for, don't you?
Piled Higher and Deeper.
I also met a few people like that (I'm just an engineer, so obviously inferior to a Doctor and I should just acquiesce to whatever my obvious superior is stating, however stupid). Usually their attitude does not last long (I like to think I know what I am talking about and the intelligent ones realise it), or I just ignore them and don't work with them anymore.
And about being a mechanic, I've met mechanics - called mechanical technicians in my field - to whom I always listen and would not dream of contradicting in their field without a VERY good and convincing reason. These guys know what they are talking about and were WAY more experienced than me. I don't care about diploma; the only times I had to correct what they were saying is when they did not have all the information and I learned a lot from them.