This time it's King Baasha that he's pissed off about. Baasha became king by killing Jeroboam's son, Nadab, and then slaughtered the rest of Jeroboam's family, "according to the saying of the Lord."
Now you'd think that God would thank Baasha for doing his dirty work for him. But if so, you'd be wrong about that. God was angry at Baasha for killing Jeroboam's family, even though he inspired him to do it. God works in really creepy ways.
God made his plans known in the usual way: he sent a prophet (Jehu) to tell Baasha the bad news.
Then the word of the LORD came to Jehu ... Behold, I will take away the posterity of Baasha, and the posterity of his house; and will make thy house like the house of Jeroboam ... Him that dieth of Baasha in the city shall the dogs eat; and him that dieth of his in the fields shall the fowls of the air eat ... for all the evil that he did in the sight of the LORD, in provoking him to anger with the work of his hands, in being like the house of Jeroboam; and because he killed him. 1 Kings 16:1-7
Yep, that's right. God will kill everyone in Baasha's family and feed their bodies to the dogs and birds.
But God doesn't do anything to Baasha. He just waits for him to die and then has his family slaughtered to teach him a lesson. (The best way to teach a man a lesson is to kill his family after he dies.)
So Baasha slept with his fathers, and was buried in Tirzah: and Elah his son reigned in his stead. 16:6
After Baasha died, his son Elah was king for two years. One of Elah's captains (Zimri) was selected by God to do the killing. First he killed Elah (while he was "drinking himself drunk") and then all of Baasha's family and friends -- all those that pissed against a wall, anyway.
His servant Zimri, captain of half his chariots, conspired against him ... drinking himself drunk ... And Zimri went in and smote him, and killed him ... and reigned in his stead....
When he began to reign ... he slew all the house of Baasha: he left him not one that pisseth against a wall, neither of his kinsfolks, nor of his friends. Thus did Zimri destroy all the house of Baasha, according to the word of the LORD, which he spake against Baasha by Jehu the prophet. 16:9-12
So God had all of Baasha's wall-pissing friends and family killed. It doesn't say how many that was, so I'll just guess 20: 10 friends and 10 family members.