Possible Clues:

• 2-star rating — and you can't get lower than that
• Under the most unfavorable circumstances
• In the least favorable case
• In the most dire circumstance
• Answer couple with consecutive letters, most pessimistically
• If everything fails miserably
• A couple relax; drained of energy, to be pessimistic
• 'If all else fails ...'
• 8's not begun, surprisingly, with glass completely empty?
• A number on side street taking the most negative view