Why do liberals get so irate whenever anyone holds them to the standards of civility they force upon the Right?

What I find so fascinating is that all the left can espouse is "the tea party did this or that vile act" when in fact, they cannot support their statement with facts. Yet, critical thinking Americans can find case after case of a left loony committing vial acts against their common man and the left always has an excuse. The most recent, the lefty who told a TeaParty member he was dead after speaking at a town hall meeting held by Christine Amanpour.