"The good of our soul is more important than the good of our body; and we have to prefer the spiritual welfare of our neighbor to our bodily comforts.. If a certain kind of dress constitutes a grave and proximate occasion of sin, and endangers the salvation of your soul and others, it is your duty to give it up... O Christian mothers, if you knew what a future of anxieties and perils, of ill-guarded shame you prepare for your sons and daughters, imprudently getting them accustomed to live scantily dressed and making them lose the sense of modesty, you would be ashamed of yourselves and you would dread the harm you are making for yourselves, the harm which you are causing these children, whom Heaven has entrusted to you to be brought up as Christians." (Moral Problems in Fashion Design Pope Pius XII)
"Yet, no matter how broad and changeable the relative morals of styles may be, there is always an absolute norm to be kept after having heard the admonition of conscience warning against approaching danger: style must never be a proximate occasion of sin." (Pope Pius XII, "Moral Problems in Fashion Design", 1957)
Pants are a proximate occasion of sin for men. They just are!
Putting the encyclical in the library.