A clever way to insult somebody, especially a slutty girl. You can't get in trouble for this because teachers are so wrapped up in useless shit (see algebra) to realize that is you reverse the vowels in both words, you get Skank Bitch.
A sink bath is where you run the faucet and go to town with your "unmentionables" via a wet paper towel to get your hygiene up to date; preferably not in the company of strangers. However most "sink baths" are in public and either spur of the moment due to circumstance (understandable) or a last result of a rock bottom situation you found yourself in. Either way you deserve to be walked in on and made a sign about.
There were no other options in my immediate surroundings to remedy my savage body odor. Alas a public restroom was made available and I took a sink bath to ensure I was fresh for the rest of the night.