Antonyms for the phrase "cleaning off" include "dirtying up", "messing up", "covering", "smudging", and "griming". These words convey the opposite meaning of cleaning off, describing the act of making something dirty or cluttered. If you want to emphasize a counteraction to cleaning off, you might use phrases like "spreading the dirt," "smearing the grime," or "tainting the surface." The antonyms can have many different connotations depending on the context in which they are used. As such, it's important to choose the right word to suit the meaning you wish to convey correctly.