See 12. Ohio election law makes it illegal to do so in campaign ads and literature.
If I see McEwen on the street, it might be etiquette-appropriate for me to call him Congressman. It is not appropriate OR LEGAL for the McEwen campaign to call him Congressman in campaign ads. It implies incumbency and gives a sense of some kind of entitled superiority, which is one of the things I find very troubling about McEwen anyway.
So are you saying if you're the encumbent that entitles you to some "sense of superiority" but if you're a former congressman your not. I can't understand why he shouldn't be allowed to have people call him congressmen in his ad. I don't care what he calls himself. People should learn to vote on a person not whether he's an incumbent.