Somebody misread a question today on SU and gave an answer that wasn't applicable because of it. I downvoted and commented on it but know I feel kind of bad about it. I think it would be better just to use a comment to notify the poster about the mistake and then maybe they'll move to delete their own answer.
If they misread the question and the question itself is inarticulate, messy or just a plain hot mess, then a comment should do.
But if they answer and totally misread it with a clearly worded and/or well written question, or if the answer is patently not even close to the same track and field as to where the question is, then downvote them as well.
I know I've misread a few questions and been punished for it, but I'm learning to read questions much more carefully.
Your suggestion of a comment is fine, but it won't guarantee an inappropriate question is deleted.
Can an inappropriate question be flagged as such, and appear somehow different, or even be hidden like 'excess' comments are?
If the question isn't clear about it's purpose, edit it. The OP will then get a better quality of answer, than they would otherwise get. After all, good quality questions, generally receive good quality answers.
If the answer is just way out in left field, down-vote or flag, until you are satisfied.
If it is only slightly wrong, edit it until it is correct.
I would comment on the incorrect answers, that they should re-read the question. Regardless of what other actions I have taken.
If all else fails, flag for moderator attention.