John Frémont in 1856 was worse. He got third place in his home state of California, about 19% of the vote and almost 30% behind Buchanan. Here's some more info for you. Yeah, Romney's result in Massachusetts really was that bad.
Millard Fillmore also got creamed in New York that election, coming in third 26 points behind Buchanan. I know he was the third wheel of the election, but it's probably worth mentioning since he did manage to carry a state and over 20% of the popular vote.
In less diluted races, Adlai Stevenson lost Illinois by 19% in 1956, and Herbert Hoover lost California by 21% in 1932.. what's Romney officially at now, 23%?