Definition from Wiktionary, the free dictionary
dittohead (plural dittoheads)
- (US, slang, pejorative) One who agrees with an idea mindlessly, especially those who agree because they are supporters of the person who started the idea.
- (US, slang) Someone who is a fan of Rush Limbaugh's radio program.
- (US, slang, pejorative) A person who agrees with Rush Limbaugh unquestioningly.
- It'll probably never happen, but if Rush Limbaugh and his clear-cut-crazy dittoheads could see this hauntingly beautiful documentary, even they might start choking on one of his favorite epithets, "environmental wacko." 
- The Seattle Times. "On a mission to save America's natural majesty". Pg. H23. October 1, 2004.