Google's fill-it-in-for-you feature when you begin typing your search shows what the most likely choices are, i.e. the ones that other people tend to enter when they start a search like yours. Let's use this to see what the most popular perceptions are of male and female nature.
"Why are boys" -- so stupid, so dumb, so mean, mean to girls they like, so confusing, so complicated, so hard to read, so immature, so weird.
"Why do boys" -- like girls, like breasts, like virgins, like to tickle girls, like to eat girls out, get morning wood, get hard, tease girls, cheat, cheat on their girlfriends.
"Why are guys" -- attracted to breasts, hard in the morning, so stupid, such jerks, such douchebags, mean to girls they like, so confusing, so complicated, players, afraid of commitment.
"Why do guys" -- (pretty much the same as with "boys," but also) get boners, like asian girls, like skinny girls, like long hair.
"Why are men" -- (so) attracted to breasts, attracted to women, stronger than women, taller than women, (so) stupid, so selfish, so mean, players, afraid of commitment.
"Why do men" -- (nothing that hasn't already been covered).
Nothing too surprising here, but notice how, contra the stereotype of easy-to-read males and super-perceptive females, these female googlers are puzzled by male behavior -- at least by the behavior of the small fraction of males who they're actually interested in. Such guys have plenty of options, so of course they're going to be cautious of who they commit to, are going to play games, and will be hard to read. In contrast, guys with no options have only one thing in mind, are desperate to play no games at all, and are as easy as a book to read.
Also notice how surprised girls are that boys would "like to eat girls out." i mean... so you don't, like... think it's yucky? ... whew!
"Why are girls" -- so hot, so stupid, so complicated, so confusing, so emotional, always cold, so mean, so mean to each other.
"Why do girls" -- wear bras, wear thongs, get tramp stamps, cut themselves, have periods, smell like fish, play hard to get, like bad boys, like jerks, like tall guys.
"Why are women" -- so stupid, crazy, so emotional, always cold, so complicated, so difficult, attracted to bad boys, called cougars.
"Why do women" -- get wet, nag, cheat (on their husbands), stay in abusive relationships, have abortions (among other things already covered).
Again nothing too surprising, although notice the paradox that females are seen to be so cold and also so emotional -- namely around dorks they wish would leave and around everyone else, respectively. Also, girls are not just "mean" or "so mean" to the opposite sex, as guys are, but girls are also "so mean to each other." Even if they've seen Mean Girls, most guys have no appreciation for how destructively catty the average girl is, although girls will readily admit it if you ask them about it and say they wish it were otherwise.