The film biz all about chemistry: some actors have it, and some don’t. The likes of Astaire and Rogers and Martin and Lewis made their name as a double act, a combo you could throw into any plot, any predicament, and come out with celluloid gold (or something that would turn a profit, at least).
Sometimes, though, a pairing leaves you scratching your head. To throw certain sets of actors onscreen together can seem like a disaster waiting to happen. There’s no way they’ll compliment one another, play off each other well. This can be down to egos, contrasting styles, or plain old bad writing.
A weird onscreen duo isn't always a bad onscreen duo - take De Niro and Jerry Lewis in The King Of Comedy, for example. For the most part, though, the signs are obvious enough from the poster: two stars the studios are trying to cram together, for whatever strange reason they’ve dreamed up.
Sometimes they’re great, sometimes they’re complete stinkers. And sometimes, when concept and casting are sufficiently bizarre, they simply fade away into the ether.