"...And howcome when a man stands up while peeing it's normal, but when a woman does it it's weird?"
--South Park
When it comes to feminism I often see the term 'double-standard' being used to dismiss an issue that goes beyond equality. I'm all for treating women equally, but we have evolved in such a fashion that Women are very, very different from men.
The best example I can think of is that of adultery. Is it a double-standard that an adulterous man, while still given a hard time about it, gets off lighter than an adulterous woman? I'd have to say no, despite being raised in middle-class, white society where we are taught everybody everywhere is absolutely equal (unless they're fat, in which case they're weak willed). If you're a feminist (which I would hope most people are, men included) you might be offended by this, so I should explain myself.
When a man cheats on a woman he is expressing his desire for variety. He is showing that he still has a libido. A man fucks another woman because they are another woman, not because there's anything particularly special about them.
When a woman cheats on a man it's because she is unsatisfied, or sees the other man as a better specimen. Generally speaking a woman does not cheat on someone when she is satisfied and a woman does not cheat on someone if she perceives them as superior than the man she is considering cheating with.
One needs look no further than evolution to see why a woman's adultery is so insulting to a man. A man benefits genetically from adultery because back before we had contraception being adulterous meant spreading your seed. A woman, on the other hand, benefits from adultery because she upgrades from her partner. A man is simply putting his seed wherever he can whereas a woman is looking for the perfect seed to be implanted with.
In essence, when a man cheats on a woman the best thing he is able to say (while still being honest) is "I love you more than these women, but am weak-willed" when a woman cheats on a man the best thing she is able to honestly say is "I love you. But not as much as I love Edwardo, our pool cleaner."
Then again I could be absolutely wrong, it wouldn't be the first time.
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I think I should also add that a double-standard is not necessarily a bad thing. I think there's a tendency to interpret 'double-standard' as meaning 'two groups of people are treated differently because of irrelevant things'. This is the case some of the time, but I think you'll find there are quite a few double-standards you wouldn't want to get rid of, for example, the way we allow soldiers to drive tanks but not civilians.
'Do as I say, not as I do' is a good example of a positive double-standard, especially when talking about addictive substances. It may seem hypocritical to have a smoker tell you not to smoke, but what needs to be understood is that the cause of the addiction is the same as the effect: Smoking, the cause, a one time thing the smoker regrets, is what the smoker is speaking out against; not the effect which just happens to be continued smoking.