Similarly, the recent-ish trend of "open in app" buttons that obscure the content drive me crazy. Imgur does this. It's already open in my app, I prefer my browser as the "app", thanks.
My personal favourite is facebook chat. Mobile site? "You have to use the app!" Request desktop site? Well well well, it appear to work just fine. Supremely annoying the one time a month I need to reply to someone's message...
Even if it's a little bit primitive, the facebook chat at mbasic.facebook.com still works when you need it.
I just hit the aforementioned "Request desktop site", which works fine as well.
Extra irritating because it offers that app on every mobile browser, including those run on an OS they don't have an app for.