Definition
A humorous expression used to indicate that someone has used a rude or offensive word, often as a lighthearted reprimand.
"You used that word? You better go wash your mouth out with soap!" Mom said jokingly.
Hearing him blurt out the word, she jokingly said, "You better wash your mouth out with soap."
When the child said a swear word, the grandfather said with a chuckle, "You better wash your mouth out with soapy water."