From the Toddlerspeak Dictionary, Gabe's Edition
fing n. Bath. v.i. To bathe.
["fing"=swing, corrupted from "fim"=swim.]
Ex. "Ohn fing!" ohn I want, I want to + fing a bath, to bathe, to swim.
Used in increasingly desperate and voluminous tones upon observing an older brother who, in consequence of a broken arm in a plaster splint, cannot shower like everyone else just has, and must bathe in Mom and Dad's superfun big tub.