While not excusing bad temper or impatience or garden-variety snark, I would offer that it does wear on one to keep answering (or defending more like) the same questions - and not just from RCs, but Protestants as well ("You worship Mary! And idols! And call men 'Father'! And think your works will save you!")
Also I have noticed a sort of attitude on the part of RCs that it's only a matter of a few details that separate us. And if we Orthodox would only quit being such soreheads and so unreasonable everything would be hunkydory. That naturally rankles a little.
I understand where you are coming from, and I agree you have heard many of these statements or arguments many times, but also remember the inquirer may be noting these observations for the first time. Aside from addressing Orthodoxy, let me relate to a somewhat similar comparison from another perspective. Over the past 30 yrs I have trained hundreds of people in my particular profession, and from novices I usually get the same questions. They are starting from zero, not the years of experience I have, so I can't expect them to have the same background experience to pull from, that I have. Granted, they should ask questions respectfully, but then again they may not feel they are being disrespectful. back to Orthodoxy, many stumble on to it and want to get all the "but why" questions answered in a paragraph. Could just be enthusiasm.