"Consider going into a classroom and looking around, and you’re the only man there. Even if you’re totally ok with that (heck, you expected it), you notice. You feel all the women in the room notice you and see that a lot of them are glancing over at you or making comments about your presence. Ok, you knew that might happen. A woman next to you says, “Hey, cool, a guy in a CS class, good for you.”
When it comes time to form a study group, half the women in the class don’t want to work with you because they assume men aren't as good at CS. The other half jockey to work with you, some for the novelty (“Hey, I’m in a group with the guy, “) and half because they want to ask you out.
When you go to apply for an internship, a lot of companies seem really interested in you, but you’re not sure if it’s because they like your resume or just because you’re a guy in CS and they want to look open and forward thinking by having lots of male interns coding. You meet up with a group of female interns and one makes a slightly sexual joke. Everyone freezes and looks at you - are you one of those guys in CS that is serious and can’t take a joke, or will you be one of the girls? At your job after you graduate, it’s naturally not ok for a woman to say outright that she’s prejudiced against male coders… But maybe your boss gives you slightly different work, or it takes longer for you to get a promotion because they need more proof that you are good - you don’t get the benefit of the doubt the way the girls do. When you express a strong opinion about a tough problem, the women write it off as you being sensitive and emotional - men often are, you know. When discussing your career ambitions, your coworkers often ask you how children play into that - I mean, you’re probably looking for a wife and plan to have kids since you’re in your late 20s. Everyone knows it’s a safe bet that kids are going to derail your career at least temporarily, if not permanently. You frequently police how often you mention family at all for fear people will assume you’re expecting a kid soon…
… Does this begin to explain it, at all? Even when a company is open to women working in all areas and no one is a dick, there is still a lot of pervasive bias that affects how women are treated and perceived. Why would you notice? It doesn’t affect you."