swim:
S-someone
W-who
I-isnt
M-me

Someone Who Isn't Me. Most people use this abbreviation when telling some story about them doing something unsavoury, to avoid reprimand.

someone
who
isn't
me

commonly used to avoid self incrimination in contexts such as boards discussing drug use. also used in places where generally criminal acts are taking place. (not dissimilar to use of illicit drugs)

m is sometimes replaced with y (for you) wherein someone would be questioning another.

a fancy way of trying not to drown in any given water

Swim = Somebody Who Isn't Me

Acronym for:
Sorry
Wrong
I (instant)
M (message)

Used when you IM someone other than the person you were trying to IM.

code word to smoke weed