To have lost a competition or goal for a prized object or person (girl, grade, money, presidency) due to terrible and negative planning, tactics, and broadcasting. Stems from the 2008 presidental election between Senators John McCain and Barack Obama, wherein John McCain was delivered a crushing defeat argurably due to negative campaign and debating.
As an verb: "Cindy did nothing but party the whole weekend when she should've been studying on her finals. She McCain'd her test and now she has to retake the course."
As an adjective: "Derrick totally got McCain'd by Juile because not only did he show up late to their date, he also showed up naked."