Mine came being King of Italy, which I got beginning as count of Empúries (later count of Provence, later came conquests and wars, inherited Tuscany and Apulia...). At the end, I had 6 bad kings in 24 years. Ermenguer III, Gausfred II, Gausfred III, Berenguer II, Gausfred IV, Gausfred V. The last two were cousins of the formers, and the kingdom of Italy fell on the head of a foreigner, because of a bad marriage movement. William de Hauteville was crowned king of Italy, and when he died, the heir was the king of Sicily, Roger de Hauteville.
Damn it!
Shortly after, I saw how the only living members of my dynasty, the 75 years old count of Rosselló, and two kids, one of the new-born, died within three months. When my last living character, Gausfred, died, game over. Althoug, I have to say, he died in battle fighting the king of Sicily and Italy, and I offered vassalage to France. Too late, though.