Single-sex restrooms have their uses in some settings; obviously in a more public setting like a mall or movie theater or the like unisex bathrooms would probably work out fine, but making them the rule rather than the exception could cause problems. In the dorms at my university, for instance, each floor has one restroom for males and one for females, each with four showers and six stalls (in the men's room, at least; I'd assume the women's room would have more stalls in place of urinals). As someone mentioned earlier, the lines for men's rooms tend to be much shorter than women's rooms--in this case both for the stalls and the showers, even though there are many more males than females in most dorms--so from a purely selfish perspective the guys on the floor likely wouldn't want to share with the girls. Also, this being a college setting, I doubt people would be mature enough to handle that much mixing of the sexes; many of the guys in my dorm freshman year were still in the "see girl, stare at chest, make lewd comments, find new girl, repeat" stage of male/female relations, so I don't see a unisex bathroom turning out well at all there.

Finally, and most importantly: To save time in the morning before classes, most of the guys in my dorm would just roll out of bed in their boxers and stand around in the bathroom slowly waking up while they waited for a shower stall to become available. They wouldn't do this if there were any girls in the bathroom. You wouldn't be so mean as to deny me and other gay guys the lovely view, would you?

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Off topic, an update on my situation (recap: met boyfriend "J", neither set of parents know about us being gay, J was unexpectedly outed to brother "R" on Valentine's Day, R threatened to tell parents, hasn't returned J's calls since):
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J got a hold of R yesterday evening after two weeks of the silent treatment and was finally able to have a calm, rational conversation about it. Fortunately, R hadn't said anything to the parents yet; he had just kinda freaked out to find out that his frat-boy, womanizing, sports-loving brother had turned out to be gay, defying all the stereotypes ("The gays! They're everywhere!"), and after hanging up he felt bad enough about the reaction that he decided not to tell the parents immediately. Apparently, over the past two weeks R had gone to a few parties at his own fraternity where his friends had made a bunch of homophobic remarks as usual, and when his first internal reaction this time wasn't "Yeah, ha ha, gay jokes are funny!" but rather "Hey, that's my brother you're insulting!" he had a major wake-up call.

R still doesn't want to talk to J about it since he still finds it really awkward, and he's made J promise not to tell any of their mutual friends about "the gay thing" so it doesn't reflect badly on R , and he still made a few homophobic remarks during the conversation (no one insults R's brother but him, apparently), but...on the whole it seems like things turned out okay-ish. Two steps forward, 1.5 steps back, I guess?