Oh, Marshall Mathers
Shithead with a potty mouth, get the bar of soap lathered

from Eminem – Berzerk Lyrics on Rap Genius

Meaning

A potty mouth is someone that curses a lot, and Eminem definitely satisfies these prerequisites.

A common punishment for a child that swears is for his/her mother to wash his/her mouth out with soap. Therefore, Eminem is telling us to get the soap ready for when he starts swearing again.

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