This isn't the first ad of its kind I've seen on SO. there was another a while ago that confused users by imitating the tab-style layout of the SO navigation.
Any ad that attempts to trick people by imitating site content, or pretend it's not advertising, is underhanded.
Attempting to weasel out of that with "but WE'RE not doing that, we're IRONICALLY poking fun at people that do that!"
... well, maybe you're doing that as well, but you crafted an ad that imitated site content to do it, so mainly you're engaging in the very activity you're deriding. slightly clever, but wholely hypocritical, and still underhanded.
it annoys me that a site I enjoy as much as SO allows advertisers to use these tactics.