Crusader Kings II: Italy
I noticed that one of my courtiers, who I invited to court earlier beause he had a strong claim to the Kingdom of Italy, was the heir to the Kingdom of Pomerania. I normally hesitant to initiate a plot to kill because half the time, my complicit is revealed but I thought it was worth it. So, I landed this courtier with one of my two spare baronies and initiated the plot. Good news: assassination went without revealing the mastermind (moi) but instead of being my vassal, my new baron became an independent king! Gah, why? It is now that I suspect it's because he inherited the kingdom, rather than me pressing his claim. So since his inheritance title (king) is higher than his then current title of baron, he became an independent king, taking along the barony. I felt dissatisfied with the previous outcome and wanted to declare war on Italy just to get back my barony. It would have started the first world war though haha. Better idea is to simply press a claim on Italy for a vassal....