Full of confidence; having strong faith in one's own ability or judgment — sometimes implying overconfidence.
彼は面接で自信満々に話していたが、結果はどうだろうか。
He spoke in the interview brimming with confidence — I wonder how it turned out.
自信満々にプレゼンを始めたが、質問に答えられず狼狽した。
He began the presentation full of confidence but became flustered when he couldn't answer the questions.
彼女は試験前日に自信満々だったので、余裕を感じているようだった。
She was full of confidence the day before the exam and seemed relaxed.
自信満々の態度は時に反感を買うこともあるので注意が必要だ。
A very confident attitude can sometimes arouse resentment, so be careful.