501

When I was a teenager you could buy Wranger or Levi jeans with zip-flies, and they fitted perfectly. My preference was for Wranglers.

Since the retro introduction of the button-fly jeans, such as Levi 501s,  in the late 80s and 90s, you now have the option of perfectly fitting jeans with a pain-in-the-arse button-fly, or ill-fitting jeans with a zip-fly.

Going for a pee in button-fly jeans takes about half an hour, for heaven's sake.