Possible Clues:

• 'What was I thinking?'
• 'What a fool I am!'
• "D'oh!"
• Words before 'And here I thought ...'
• ''I should've known better''
• ''What a fool I am!''
• Verbal alternative to a head slap
• [Headslap]
• "I was so foolish!"
• 'Gosh, what was I thinking?!'