Possible Clues:

• ''Et tu, Brute? Then fall, Caesar!,'' e.g.
• They might come back to haunt you
• Theme of this puzzle
• Things historic figures were going to say
• This puzzle's theme
• "I'll believe it when I see it!"
• 'Like you're really going to do that'
• Passing comment while couple occupying farm sold us ground
• Something memorable said in passing?
• Say "Kiss me, Hardy"? Don't tempt fate!