The content below is entirely editable.
The character is head over heels of him -or herself. He/she might be the best(or not) , but usually the laziest to act and always underestimates the enemies. Rather popular concept for villains and rivals.
An often used concept of depowering a character. The character has such confidence and high regards of his/her abilities that he/she unjustly underestimates the enemy. It's a CIS(character inducted stupidity) which eventually leads to his/her defeat somewhere in the story.
Sometimes it's used simply as a comic relief where an obviously weaker person is boasting about his/her abilites or in extreme cases he/she finds excuses of not accepting the defeat.
Arrogant characters' high self-esteem often borders idiocity and so the comically arrogant characters are usually as their name suggest are comic relief devices, for purposes hardly more than for laughs.