dirty

   1. pertaining to anything harmful or damaging which may be the subject of a taboo

   A dirty (atomic) bomb is going to go on killing more life for a longer period in a nastier way than a clean one. A dirty joke usually involves copulation or homosexuality. A dirty book may be itself clean but contains pornographic or salacious material. The dirty deed is extramarital copulation by a male:

    ... my mind leaped to the conclusion that he had taken her from me, and done the dirty deed on her. (Fraser, 1977)

   A dirty old man seeks a sexual arrangement with a much younger person. A dirty weekend may be fine and sunny but is passed in overnight clandestine copulation:

    They've simply gone for a dirty weekend at the Spread Eagle. (Matthew, 1978)

   See also clean¹.

   2. to urinate or defecate (while wearing clothing or recumbent)

   In phrases like dirty yourself, your pants, or your trousers. They are not used of splashing with mud.

    ... patients could only be kept lying on sand or sawdust, because they perpetually dirtied themselves. (Burleigh, 2000)