OK, so you can post something stupid anywhere. But there's something about Twitter's rapid-fire, 140-character bursts that brings out the stupid in people.
From companies embarrassing themselves to celebrities behaving badly, it's hard to name just one Twitter doofus. But here are a few nominees:
• Chris Brown, the hip-hop star, consistently used Twitter to make himself look like a foul-mouthed rage monster. Instead of thanking fans after winning a Grammy, he launched a profanity-laced bromide at his "haters." Then there were the misogynistic, scatological insults he hurled at comedian-critic Jenny Johnson before "quitting" Twitter. (He's back.)
• McDonald's thought it would get a little of that social media love it had been hearing about in January when it created the #McDstories hashtag -- asking customers to share their favorite McDonald's memories. Then it found out what happens when you give the Internet open access to your advertising effort. McDonald's yanked the campaign after just two hours and countless food-horror stories about fingernails, insects and bouts of food poisoning.
• Spike Lee was, like many Twitter users, angered by the killing of Florida teen Trayvon Martin. Tweeting the home address of shooter George Zimmerman would have been questionable enough. But Lee mistakenly tweeted out the address of a couple who have a son by that name. They had to leave their home after being besieged by reporters and threats. Lee would later apologize and "reach an agreement" with the aggrieved family.
• Greek triple jumper Paraskevi Papachristou was on her way to the Olympics when she tried a little ill-advised Twitter humor. With so many African Olympians in London, "the West Nile mosquitoes will at least eat homemade food!" she wrote. Her tweet was quickly criticized as racially insensitive, and Greece's Olympic Committee barred her from participating in the Games.
• Oprah Winfrey had been gushing for weeks about how much she loved the new Microsoft Surface tablet, culminating in this tweet: "Gotta say love that SURFACE! Have bought 12 already for Christmas gifts." Unfortunately for her, those words were followed by ... "via Twitter for iPad."