"A person could piss against a tree, he could piss on his mother, he could piss on his own breeches, and get off, but he must not piss against the wall -- that would be going quite too far. The origin of the divine prejudice against this humble crime is not stated; but we know that the prejudice was very strong -- so strong that nothing but a wholesale massacre of the people inhabiting the region where the wall was defiled could satisfy the Deity." -- Mark Twain, Letters from the Earth
The phrase "pisseth against the wall" occurs six times in the Bible. It is generally used to describe the killing of all of the males in a particular group of people.
David used it when referring to Nabal and his household.
(Nabal's wife, Abigail, saved the wall-pissers in her husband's household by bribing David. Later God killed Nabal so that David could obtain Nabal's wife and other stuff.)
So and more also do God unto the enemies of David, if I leave of all that pertain to him by the morning light any that pisseth against the wall. 1 Samuel 25:22
Surely there had not been left unto Nabal by the morning light any that pisseth against the wall. 1 Samuel 25:34
God told Jeroboam's wife that he would kill everyone in Jeroboam's family (and their descendants) who pissed against a wall.
(The message was delivered by the prophet Ahijah to Jeroboam's wife who was trying to save her sick son. Ahijah told her that God would kill her son by the time she got home. God did as Ahijah prophesied.)
Behold, I will bring evil upon the house of Jeroboam, and will cut off from Jeroboam him that pisseth against the wall. Thus did Zimri destroy all the house of Baasha, according to the word of the LORD. 1 Kings 14:10-12
Zimri killed all of the wall-pissers among Baasha's family and friends, "according to the word of the Lord."
(Zimri was later burned to death for doing God's dirty work in the Baasha killing.)
Zimri ... slew all the house of Baasha: he left him not one that pisseth against a wall, neither of his kinsfolks, nor of his friends. 1 Kings 16:11
God killed everyone in Ahab's family that pissed against a wall.
(Because Ahab allowed a captured king to live.)
Thus saith the LORD ... Behold, I will bring evil upon thee, and will take away thy posterity, and will cut off from Ahab him that pisseth against the wall. 1 Kings 21:19-21
For the whole house of Ahab shall perish: and I will cut off from Ahab him that pisseth against the wall. 2 Kings 9:8