This is our shower curtain.

One of the nuclear waste warnings.

Edit: https://en.m.wikipedia.org/wiki/Long-term_nuclear_waste_warning_messages

Get a picture of yourself taking a shower. Print that onto the shower curtain.

One with your face printed on it.

Plain curtain. Cut a hole about 3 inches in diameter, about 30 inches from the ground. Line the inside of the hole with duct tape.

I'm sure there are hentai shower curtains

A shower curtain of After Dark Flying Toasters

None whatsoever.

White one with brown/yellow shading near the bottom to make people think it's dirty, but it's not

1. Take a normal shower curtain and have at it with a long kitchen knife. The knife cuts won't let very much water through so it will still be effective as a shower curtain.
2. Take a stray can of red paint and spray be a few two or three long strokes across it.
3. Only attach the rings of one end to the shower rail up to one half at most. Break the remaining rings and leave them on the bathroom floor.

Velvet.

The full text of the communist manifesto in fine print on the inside and this on the outside:

I once saw a local Zillow listing with a very graphic gay bdsm shower curtain. So you can buy that somewhere, but that's a Google search I am not about to make for you.

One that is way too short

A semi-translucent one with the blurry silhouette of people making out printed on it.

Staple a tarp to the ceiling so it hangs down in front

A DIY one made from cardboard

beads

A shower curtain of a very important, and well known document from your country such as the Charter of Rights and Freedoms from Canada, or Declaration of Independence from the US. If you live in a country that still recognizes the British monarch, you could also put up a photo of the king (very common in government and military buildings)

A picture of a masturbating man inside (ideally you)

window blinds

The one with you naked since it defies half of the purpose.

A photo of yourself, naked, in that very shower. With your dick enlarged to a comical size. (Or shrunk.) (Yes this is a gender neutral suggestion.)

asking the real questions

human skin

A transparent one