Shall I call him a Professor? He's not even teaching anymore.?!

If he has a doctorate, of any sort, it is polite to call him "Doctor", professionally. For social occasions (inviting him to your cocktail party, for example), "Mr" would be correct. "Professor" is used in the USA mostly for people who do not have doctorates. In Europe, it is preferred (or combined with) "Doctor". In other words, stick with "Doctor" unless you learn that he prefers something else.

This has nothing to do with authority over you or whether you are a baroness. It is simply professional courtesy. Show some.

"Dude" is what i would call him.

I would normally call a person by his official title given by the employer. If your hospital is calling all professional doctors as Doctor and he is employed as a Doctor (and not Professor), then by all means Call him Dr.So-and-so. Just because he was a professor back in his country does not mean he is a qualified professor in your country. If he insist to be addressed as 'Professor', it means he's an old school and would prefer to distinct himself a little higher above the rest the other doctors. I would call him a Professor alright.. with plenty of sarcastic tone to it.

And no, a land baroness does not mean you are a baroness either. It means nothing nowadays.