Possible Clues:

• Sounds as if the part of this is that it's a mistake
• Boss not right, making embarrassing mistake
• Howler
• Chief electrician finally sacked for indiscreet remark
• Such a blunder for 12 across to use this, by the sound of it
• Faux pas made by boss endlessly
• Boner
• Brick (that's dropped)
• Socially awkward or tactless act
• Foreman nearly makes a blunder