People who irk me:
Nannies that lecture me about safety. I notice that it is usually the ones who have no idea how to solve problems that like to go around prattling about safety.
Professionals who recommend hiring a professional. Hello, it's a do-it-yourself forum. Take your tradesmanship chauvinism somewhere else.
Naysayers who go around like Glum the Lilliputian explaining how the project idea will never work.