I write and, to a lesser extent, read crossovers all the time, and this is one I haven't stumbled across yet (maybe I'm reading the right stuff?). But no wonder it's one of your pet peeves. How obnoxious. Especially if you see it again and again.

Though I will admit that I have this epic never-will-actually-be-written story in which Joyce Summers marries Keith Mars, and Buffy and Veronica kill vampires and solve crimes together and and Wallace and Mac hang out with Willow and Xander and Spike falls in love with Veronica and Logan falls in love with Buffy, and it's all very, very snarky and epic.