Or boyfriend! Password sharing is a lynchpin of intimacy in the 21st century—and it can be complete nightmare unless you're savvy. So when should you do it? And for what?
In general, don't even think about giving up that super-secure string of 64 randomly-generated characters until you have a real relationship on your hands. If a fling is asking for your password to begin with, it's probably time for them to be flung away. But once the toothbrush is in your bathroom, the question is inevitable: "Hey, what's your password? I need to check something." Here we go.
Yes, absolutely. If you're embarrassed by your taste in movies and TV, your relationship is screwed anyway. Don't deprive the GF or BF of leeching off of you and enjoying some streams when they aren't cuddled up next to you. Just make sure it's a different password from everything else.
No. Never. This is your private area. You talk to your family here, your coworkers here, your most intimate friends. The inbox is one of the few sacred places left online, the only space on your monitor not shared into oblivion. This isn't about having something to hide—it's about keeping meaningful boundaries in an era when there are verrrrry few. We all need whatever scraps of privacy we have left, and your email is just that.
Why would anyone ever need your email password, anyway?
See above. Sure, most of your Facebook life is entirely public (or broadcast to everyone you both know), but the inbox factor remains, and should things go south, you don't want a rogue account on your hands.
What? No. Again, nobody should be asking for this to begin with, unless they're performing a social psychology experiment that involves impersonating you.
This will come up. "Hey, what's your password, I want to find this article." There are an infinite number of innocuous reasons why your S.O. will want to use your phone, whether they're looking something up, or want to play a game. Whatever—it's harmless, and saying no sounds paranoid and standoffish. You'll have to trust him/her not to go through your inbox and texts, and they'll have to trust you not to have any incriminating texts and dick shots in your photo gallery.
See above. Your laptop will be lying around, and if your sexlovefriend is hanging out at your place, that becomes the computer. They might want to check their mail, read an internet blog, or, I don't know, one of the other trillion things you can do with a computer. It's a computer. Again, this is a mutual test of trust—but it's an important one, and a sign that you can rely on the other not to go Bradley Manning on your stuff when you aren't looking. Oh, and don't look—giving your laptop password and then staring over their shoulder is probably worse than not giving it at all.
User Manual is Gizmodo's guide to etiquette.