Possible Clues:

• Noodle or bean
• Something to knock some sense into?
• Mug about to return goods conforming to latest fashion
• Small quantity of liquor, or two other drinks
• Small measure of liquid
• Head discovered activity behind the bike-shed?
• Lack of b-booze in cup
• If one were the sort of mug to leave the stable door open, this might be the result