"Forty million readers follow the Gumps. ... If I could prove it I would say there are exactly 16,847,915 3/4 people writing to Sidney Smith, care of the Chicago Tribune, with suggestions as to what he should do with the Gumps next. And inasmuch as most of us take the Gumps seriously and expect to have our suggestions followed, the problem of these suggestions is a real one, after all."
--William Fleming French, describing an example of the problem of fannish engagement for newspaper comic The Gumps, quoted in Jared Gardner's Projections
There are really only two places you can have the villain of one major franchise sing a song from another major franchise. One of those places is in fanfiction.
But hold that thought while we talk about this image from Age of Ultron and what it can tell us about Captain America: Civil War.