I have an old house built with geometry that Man Was Not Meant To Know. While I've learned to live with the odd noises, lights and sense of impending madness, the shower curtain has been a problem. See, the bathroom walls aren't quite straight so I can't get a tension rod to stay up in place.

So, I designed this thing. The bottom rectangle is sized for a large waterproof 3M Command strip, and the top is just the right size for most standard tension rods.

Print a pair and stick up with a large waterproof 3M Command strip.

Or, if you want a different size, check out the openscad file and adjust it for your own bar.