See, I'm a bit (okay, a lot) on the sarcastic side and can be a bit rude, especially when receiving reviews for fics that the person clearly hasn't read, or at least read well, so my reply would border along the lines of:
Step One: Grammar classes. Look into taking some.
Step Two: Read fic before reviewing.
Step Three: Repeat steps one and two as needed.
But, really, I think the "HUH?" reply probably works best.
And personally, I left the Potter fandom because of how much it started to grate on me, so I think you have the right idea in just posting once in a while and avoiding all of the wangst. *nods*