For anyone who has every felt the pain train of a Sunday hangover after a weekend of binge drinking. There is nothing like a "Super Awesome Medicinal Sunday Hangover Bacon and Tomato Sandwich" (S.A.M.S.H.B.A.T.S.) to make someone feel better.
This abbreviation means "I Want You To Fuck Me So Hard I Can't Walk Anymore"
Example
Boy 1: Hey Jess, if you're a freak, then you know what I.W.Y.T.F.M.S.H.I.C.W.A
Jess: Yeah, I know what it means. I'm not that innocent. "I Want You To Fuck Me So Hard I Can't Walk Anymore"