Is said to derive from the practice of putting one's toungue to their cheek to keep from laughing.
Today it often means that someone is kidding or joking.
An expression can indicate that the writer is using them tongue-in-cheek.
acronym for the name secret internet fatty
wow there are a lot of sifs on myspace
דוא"ל יומי חינם
אימיילים נשלחים מהכתובת firstname.lastname@example.org. לעולם לא נשלח לכם דואר זבל.