Snopes.com is a thing. Bookmark it. Learn it. Use it. Love it.
If you read an email that was forwarded to you and 20 other people by one of your friends, who got it forwarded to him and 20 other people by one of his friends, who got it forwarded to her and 20 other people by one of her friends, etc, do yourself a favor: look it up.
You know how it happens. You get an email about some outrageous and unjust thing that some company/politician/whoever said or did, or that relates a heartwarming/heartrending tale of triumph or tragedy. You think to yourself, "I can't believe Obama said that!," or "Those Starbucks scumbags hate our troops!," or "Yeah, fuck Neiman-Marcus! I'm making their damn cookies for free tonight!," and then you mash the forward button to your whole address book so they can share in your righteous outrage.
Except... none of it is true. You've been skunked, either deliberately by some Internet prankster, or unintentionally by some well-meaning, but gullible, soul who just didn't do their homework. Don't be that person.
Before you rage-crush that "forward" button to fire off news of this atrocity to your 20 closest friends, go to Snopes, and see if it really happened. If you don't, I promise you, someone else will. Someone who will hit "reply all," include the link gleaned from the two minutes of research that you failed to do, and make you look like a gullible dumbass.
This especially applies to public forums and social media. People in your email circle will likely be polite about making you look like a dumbass because they are friends and family. You probably won't be so fortunate out in the wilds of the wider Internet community.
(Update: I've been told that fact-checking on Snopes can make you look like "a know-it-all jerk." Fair enough. I'm not saying you have to be the "reply all" person who calls people out for their credulity. I'm just trying to arm you, dear readers, with the tools to avoid becoming the person who gets called out for your credulity.)