I don't have anything against the "wat" posts in particular, as I dislike a broader kind of posts which seem to have been made just for the sake of posting. I'm talking about posts with just a smiley or just saying "LOL" or "I agree" without providing further arguments or anything relevant to add to the topic. I also don't like to read posts in which the poster is deliberately careless about writing in proper English. Posts are, for me, supposed to have some thought and time put into them, as opposed to what is said a chatroom.
However, when I say that I "don't like" that kind of posts, I don't mean they are disrespectful or offensive nor that they should be forbidden or that this "code of conduct" should be enforced in any way other than by setting a good example.
I do understand LPChip's point, though, about people who might have put some effort into their posts and then get a reply like that. There are certainly instances in which such replies may sound harsh and everyone should be careful not to be misinterpreted, as in a forum, unlike in live conversations, no one can tell if you are kidding by looking at your face.