The magical day before
Monday and after
Sunday. The perfect day to plan to do things you can't really afford the time to do during the week. Alternatively, anything you can't remember when or if it happened, say it happened on Smonday.
Originated from some confusion when a weekly TV guide missed the date between a
Sunday and a Monday, leaving the only explanation that the missing date fell on a Smonday.
"Do you
fancy going to the theatre this week Bob?"
"
Yeah, but I'm really busy and can't really afford it. Can we go on Smonday?"
"Do you remember when you tripped up and your wabs fell out in
front of all the guys in that club?"
"Erm... that never happened!"
"Erm, yes it did! I think you'll find it was last Smonday."