The response to the photo, at left, was apparently not what she had expected.
Just one hour after she posted the picture, a seemingly hurt and angry McCain posted this tweet: "so I took a fun picture not thinking anything about what I was wearing but apparently anything other than a pantsuit I am a slut, this is."
And then this one: "why I have been considering deleting my twitter account, what once was fun now just seems like a vessel for harassment."
And then this: "when I am alone in my apartment, I wear tank tops and sweat pants, I had no idea this makes me a "slut", I can't even tell you how hurt I am." (Here's McCain's twitter page.)
McCain, who writes a column on the Daily Beast Web site and has more than 60,000 twitter followers, quickly took the photo down. But it had already spread far and wide online and generated enough interest to rise, for a brief moment, to the top spot on Google Trends.
She also kept posting about the picture and the response to it.
"ok I am getting the f*** off twitter, promise not to delete my account until I sleep on it, thank you for the nice words supporters," she wrote. And then she offered an apology: "I do want to apologize to anyone that was offended by my twitpic, I have clearly made a huge mistake and am sorry 2 those that are offended."
Twitter users expressed surprise that McCain was taken aback by the response to her photo.
"I find it difficult to believe that she [didn't] expect *some* reaction to that photo," wrote afrobella. Others expressed sympathy for McCain for the criticism she received.
"i really don't understand why people r having a cow over megan mccain's pic," wrote pamela1483. "i think it's fine. whats the problem? that she has boobs?"
On Thursday afternoon, McCain wrote a pair of tweets that, taken together, formed what seemed to be her takeaway from the experience: "I would like to thank my family and friends for their support. This has been an embarrassing experience but also a learning one. I will not…be deleting my twitter account but I will be more careful in the future about my use with the medium."
McCain seems to have learned the same lesson that many young Internet users have taken to heart in recent years: Be careful what you post online.