I think "wat" or "wut" is a perfectly reasonable response to a confusing post, because it's not always just inane; it does serve a purpose sometimes.
Let's say somebody makes a crazy-sounding post that is difficult to tell whether it's serious or a joke. Then somebody responds with "wat".
If the person who wrote the initial post was serious, then they'll see "wat" as a request for clarification, and they'll explain what their confusing post meant. On the other hand, if the initial post was a joke, then "wat" will just be disregarded as a typical, inane response to the joke.
"wat" lets you indicate to somebody that their post made no sense, without being too serious yourself. In this aspect, the fact that it's internet slang is actually an advantage.
In the above scenario, if the original post was a joke, then it would be different if somebody actually replied with "What?" rather than "wat." If somebody says "What?" in response to a joke, then the original poster might then feel the need to explain the joke, and that would make both the original poster and the person who replied "What?" feel foolish.
Maybe it offended you, LP, but that's not its intent. Personally, I think it's a lot better than saying "lol wut" (pointless and neutral response to something unusual) or "what is this i dont even" (which can be rude, as it's a way of saying somebody is crazy).