Double standards are never acceptable or necessary; why would you think they are?
As far as the separation of genders, how is this a double standard? Men have a bathroom, women have a bathroom; there is no double standard. Men have a sports team, women have a sports team; again, no double standard. You're confusing a single standard (such as possessing a cock or vag for the respective bathrooms) as a double standard.
The 'double standard' requires two distinct standards which apply differently to different demographics for admittance to the same club/group/etc.
Bathrooms don't have double standards because you aren't being admitted into the same place. And while one could argue that you're both performing the same function, the mechanics are slightly different, hence the different facilities.
Now if two able bodied people were wanting to perform the same function, or exist in the same field, then there should be a singular standard yes? This is where double standards exist, when one is held to higher standards for no apparent reason, other then demographic or gender related.
Take the US Armies fitness test as a prime example. How is it that a 17-21 year old woman only needs to run as fast as a 42-46 year old man in a 2 mile run for admittance? Whereas a similar aged male needs to run roughly 3minutes quicker than she does? And when it comes to push ups, she need to do as many as a 57-61yr old male, whereas the same aged male must perform at a minimum her peak performance?
I have seen no justifiable double standard, but I do see justifiable standards.