Possible Clues:

• "Guess who's outta ideas? Me!"
• Sad declaration in a card game
• Blank expression?
• 'Beats me'
• "Couldn't tell ya!"
• Stumped response to 'Anything else to add?'
• 'Drawin' a blank here'
• 'Ya stumped me'
• Head scratcher's comment
• 'Can't help ya'