If you're looking for the actual rules of Cards Against Humanity, you can read the one sentence on the Cards Against Humanity website that tells you everything you need to know to get started. Instead, I'm going to go over the unspoken rules with you so you can be sure you're not cheating or being a dick next time someone whips out their big black box at a party.
Rule #1: Certain cards should win every time they are played, regardless of the context. For instance, "A bleached asshole" or "pooping back and forth forever." If anyone plays these white cards or their ilk, regardless of which black card you put down, you must choose them as the winner. Every time. Forever. The only caveat is if more than one trump card is played in the same round. Then you must default to "A bleached asshole."
Rule #2: If your significant other says "you're totally going to pick mine!" you sure as hell better figure out which one is theirs and pick it. If you can't figure it out, your relationship is doomed and you might as well end it now. If you figure it out and decide not to pick it because you don't think the "a bleached asshole" card is funny, you are a jerk and also deliberately breaking rule #1. If you don't want to be seen as a Cards Against Humanity cheater to the other players by unfairly favoring your significant other, you better check yourself because there are no rules to this game except what I'm telling you right now.
Rule #3: Giving answers that "make sense" should not be and is not the only
way to win. Don't penalize people for being hilariously nonsensical
just because you don't understand irony. Yes, we get it: the black card said "What's the new fad diet?" and you responded with "A zesty breakfast burrito." Great that it makes logical sense. I suppose I could muster up a guffaw, maybe two if you have low self-esteem. But if you're picking a winner, don't overlook those unsung heroes like, say, "a cat video so cute that your eyes roll back and your spine slides out of your anus."
Rule #4: Don't play the game if you're not a terrible person. The CAH tagline is "A free party game for horrible people." I find two main takeaways with this tagline: One, if you're the kind of horrible person who tries to steal intellectual property via the internet so that you don't have to lay down the $25 to buy the game legitimately, you're in luck because it also comes free. And two, if you're not horrible, don't play it.
Normally I am inclined to say that racist jokes aren't just jokes, comments about women making sandwiches really aren't funny, and making light of homophobia just ain't right. Holocaust jokes? Still too soon. Hindenburg jokes? Probably still too soon. Revolutionary war jokes? Meh, those are probably okay. Any comment that starts with "All black people..."? Ridiculous. That said, within the context of the game, you're allowed and encouraged to be horrible. The game-makers didn't include cards like "Black people," "chunks of dead prostitute," and "Nazis" for their health. You're supposed to make horrible, incorrigible, offensive card combinations that leave your whole party cry-laughing.
But if you'd rather just be a fun-hating stick-in-the-mud, that's cool too I guess.