Honestly, I don't think you should publicly chastise someone without accepting the fact that there'll probably be people who will think you're being a bit of an ass first. Using euphemistic language like "Thanks for posting!" doesn't really help at all, honestly, since it comes across as incredibly dismissive. You simply shouldn't do it unless you're ready to sack up and live with the fallout. That's why I try to post at length when I'm being genuinely critical and mean it constructively; if you ever see me make a "thanks for posting!" comment, it'll be because I'm ribbing a fellow regular or because I intend to be a dick, no exceptions.