It's simple!.. We have space between our crotch and you don't understand something!.. We are all not shower!.. Some of us are grower!.. Our penis can be equal to a size of a huge banana and also as small as your lipstick!.. It can change size it's like sponge Balloon!.. So it's easy to squeeze it in!..
haha I know. I once read that a guy who wore them thought his children would all be born with zips on their forehead lol!! hehe the look started with Hedi Slimane at Dior Homme but the way he cut the jeans was different to the mass market. He kept a lot of fabric folded up at the hem so that they didn't look too skinny. And the cut was based on a french brand at the time. (early 2000s) I think its off-putting when guys wear jeans skintight.
I have worn some skinny jeans, and there's not really a problem putting your dick in, because skinny jeans are pretty stretchy. However you should probably wear a longer shirt if you wear skinny jeans because you get a bulge that can look kind of awkward. I don't really use skinny jeans though, since I think it feels better being able to move around and not look like a penguin.
Maybe the pants are a size bigger then usual... or MAYBE the crotch area is sewed different then loose or bootcut jeans hence extra room for comfort... or maybe they wear whitey tighteys and if there not hard.. then it wouldn't be hard to hide