From Wikipedia
In 1551, Oda Nobuhide died unexpectedly. Nobunaga was said to have acted outrageously during his funeral, throwing ceremonial incense at the altar.[4] This convinced many Oda retainers of Nobunaga's mediocrity and lack of discipline. Alienated, they then began to side with his soft-spoken and well-mannered brother, Nobuyuki. Hirate Masahide, a valuable mentor and retainer to Nobunaga, was ashamed by Nobunaga's behavior and performed seppuku. This had a huge effect on Nobunaga, who later built a temple to honor Masahide
Sorry for the bad english, not my main language and i have had a beer or 2.
Im a big fan of military history, and Oda Nobunaga was the person who introduced modern warfare to Japan, which is also why Oda, he's ally Tokugawa and his main general and friend Ieyasu was so effective in taking Japan back.
I know Oda was know as The fool of Owari for his bizzare behavior, but surely that's not enough for someone to react like he did.