Alice is having a bad day: not only does she have to clean the floor while Bob
supervises her, but he's doing everything in his power to make things worse for her. He will often utter this stock phrase, or some variant thereof, possibly while knocking over her wash bucket or deliberately dirtying the floor.
There are two reasons for this treatment:
1) To establish sympathy for Alice and serve as a minor Kick the Dog
moment for Bob,
2) Alice is the real Big Bad
, and this is a closing Break the Haughty