Related Clues:

• "Silly me!"
• 'Well, that's obvious'
• 'Gee, ya think?'
• "What an idiot I am!"
• "Obviously!"
• Response to dropping donuts and so forth
• 2001 OED addition that cites "The Simpsons"
• "Am I an idiot!"
• Word spoken with a head slap
• 'Oh, of course!'
• Homer holler
• Cry accompanying a head slap
• "How could I miss that?!"
• "Everybody knows that!"
• ''I shoulda known that''