9. Thor Thinking There'd Be No Consequences Invading Jotunheim - (Thor)
During Thor's initial coronation to Asgard's throne, the ceremony was interrupted by a group of invading Frost Giants who sought the Casket of Ancient Winters, which was being kept in Odin's trophy room. As a result, the ceremony was halted and Thor was never officially made Asgard's king, which angered the son of Odin massively. Against Odin's wishes and command, Thor led a small group of Asgardian warriors to Jotunheim - the realm of the Frost Giants - to attack them for their invasion, having seen it as a breach of a long-standing peace treaty and a declaration of war. Thinking he could put an end to the Frost Giants with such a small group was naive in itself, as he was quickly overwhelmed and outnumbered. Odin was forced to step in to save Thor and his group, and the Allfather was so angry that Thor had given the Frost Giants a reason to continue the war that he scrapped the idea of making him king, stripped him of his powers and banished him to Earth. Really bright idea invading Jotunheim, huh Thor?