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1.
n. Any male indidvidual that wears a gym sock in place of a condom while engaging in anal sex with a partner that suffers from diarrhea.
Jerry is a Mudrunner on the weekends.
by Chris/ Tom October 24, 2006
 
2.
When a person believes that they are still a virgin if they only have anal sex.
Hey man did you know that Jane is a mud runner?
by Nabik June 29, 2011