Possible Clues:

• Beginning of today's quote
• 'You're preaching to the choir!'
• ''Don't remind me''
• 'You don't need to tell me!'
• 'You don't have to tell me'
• 'You're telling me!'
• 'Tell me about it!'
• ''You don't have to tell me''
• 'You're not kidding'
• When repeated, gleeful student's cry