Possible Clues:

• Diplomat's aide
• Military assistant
• This could be a case of 11 across at last and at the beginning
• Might be a case of pain for a non-drinking diplomat
• That's the case of a teetotal pain
• Does a non-drinker get a pain? That could be the case
• Endlessly offensive ambassador's a specialist in this department
• A case of pain for a non-drinker
• One on embassy staff
• The case of the pain of a teetotaller