What is 1000 Percent?

Legal Definition
1000 percent in a literal sense means to multiply by 10. This article deals with its use in American English as a metaphor meaning very high emphasis, or enthusiastic support. It was used in the 1972 presidential election by presidential candidate George McGovern who endorsed his running mate "1000 percent" then quickly dropped him. Communication experts Judith Trent and Jimmy Trent agree with journalist Theodore H. White who called it, "possibly the most damaging single faux pas ever made by a presidential candidate."
-- Wikipedia