Discuss Anonymous's answer to: Is it unusual for a step-parent or step-grandparent to insist that their step-relatives under age 18 call them Mr/Ms/Mrs.

If you wish to be polite and stay on a formal basis with the man then by all means adhere to his wishes, but in formal relationships people who do not claim you as a relative have no right to correct such things as a relative would--that might seem a bit nit-picky, but so does his insistence on such a formal title from people who seem to want to form a solid relationship IMO.