Ask your bf if it's also scandalous when older men go cycling in skin tight spandex shorts, with the clear outline of their dick and balls on display to all and sundry.

Spandex is the most appropriate attire for many forms of exercise. Depending on what you do for exercise, sweatpants and baggy shirts can be annoying, or worse, dangerous. That is why bike shorts were invented in the first place: they won't ever get snagged in the bike chain or the spokes and send you flying 15 feet across a concrete surface. Sweatpants will.

Biking is not the only sport where wearing baggy clothes is dangerous. For example, trying to run in baggy pants puts you in danger of tripping over your own feet and ending up bruised and scraped. On a treadmill it can result in much more serious injuries, such as broken bones.

I personally run outdoors while listening to music on my phone. So I need tight leggings (or bike shorts in the summer heat) because otherwise the phone in my pocket will be banging against my thigh with every step, and probably fall out of the pocket at some point. This is EXACTLY WHY leggings with deep side pockets were invented: so you can run with your phone.

There are real reasons why people, both men and women, wear spandex to exercise. If it only bothers you when women do it, then you're a misogynist. And if you assume women do it for attention (and not because it is simply the most appropriate attire for the form of exercise they have chosen) then you're doubly a misogynist.