"Careless or Dead" by the Kleptones is one of my favorite mashups. I think it does a really great job of creating humor by mixing songs from different genres. In my dissertation, I talked a lot about how the musical elements of two songs have to line up in a certain way (harmonically, rhythmically, lyrically) to make a mashup "work." But I also mention the fact that the most valued mashups are those that combine songs from different musical genres. Mixing songs from different styles and/or time periods tends to lead to a humorous outcome.
"Careless Whisper" by George Michael is hilarious all on its own. The cheesy '80s saxophone, the seductiveness of Michael's stage persona...it's so incredibly outdated that it makes us laugh and roll our eyes as soon as we hear that opening sax riff. "Dead or Alive" by Bon Jovi is from the same time period (it was released in 1986; "Careless Whisper" was from 1984). While these songs are definitely both pop music, "Dead or Alive" is more rock-oriented. The personas of Jon Bon Jovi and George Michael are also very different. I've talked about gender in mashups before, and I think this is another good example.
Jon Bon Jovi projects a masculine, "rocker" image, while George Michael's is one of soft vulnerability. These two images in juxtaposition is unexpected, and it makes us laugh. I also think that the musical "setting" ("Careless Whisper") serves to take some of the hard-rocking edge away from Jon Bon Jovi's vocals. What do you think? Agree? Disagree? Let me hear from you!