verb. (gerund) Refers to the act of intruding upon another's private property, and then proceeding to urinate all over said property. (as if marking territory)
Willis: I've always wanted to piss on the lawn at the White House. Just look in the windows of the oval office and see the look on Obama's face......
Barnaby: Nah, man, dass trespissing. Secret service'll nail yo' ass.
When one trespasses onto another's property and urinates on the latter's property.
Ladies and gentlemen of the jury, John Smith trespassed onto Cindy McKurskin's property, and then urinated all over her front yard. He, my friends, was therefore trespissing!