Freakonomics reports on research that if you are told to wash your hands you'll be more judgmental:
A team of researchers “invited 58 undergrads to a lab filled with spotless new equipment,” reports the BPS Research Digest. “Half the students were asked to clean their hands with an antiseptic wipe so as not to soil the shiny surfaces. Afterwards all the students rated the morality of six societal issues including pornography and littering. Those who’d wiped their hands made far harsher judgments than those who didn’t.” The researchers found similar results when they asked hundreds of participants to read “clean” vs. “dirty” text passages.
From the abstract of "A clean self can render harsh moral judgment" by Chen-Bo Zhonga, Brendan Strejcekb and Niro Sivanathanc, Journal of Experimental Social Psychology, September 2010:
Given the metaphorical association between physical cleanliness and moral purity (Zhong & Liljenquist, 2006), we contend that a clean self may also be linked to a virtuous self. This enhanced moral self-perception can in turn license harsher moral judgment. Three experiments found that cleanliness, whether induced via physical cleansing or through a visualization task, licensed severe judgment on morally contested issues such as abortion and pornography. Further, we found that an inflated moral self mediated the relationship between cleanliness and moral judgment.