Possible Clues:

• Opposite of 43-Across
• Something not acceptaable
• Doctor, doctor -- I'm a failure!
• 'What were you thinking?!'
• Second helping, to a dieter
• Section of Matterhorn on own? Impossible
• Possibility that's not an option
• Wrong numbers
• Running by the pool, e.g
• Joking about tragedies, e.g