The phrase is commonly associated with children and can be sensitive for adults if used. The little boy was embarrassed because he wet the bed again.
Pro Tip 2/3
Accidental Occurrence
Emphasize that bed-wetting happens by accident, and it's not intentional. Don't be too hard on her for wetting the bed; it was clearly an accident.
Pro Tip 3/3
Not Insulting
Using this phrase as an insult or joke about someone might be seen as immature or insensitive. He felt bad after making a joke about his friend wetting the bed.