Last Day Of School. This can be used for high school seniors, college graduates, or even middle school graduates (but does that really count?). This is typically used on calendars or in sms format.
Abby: OMD BRENDA LDOS!!!! HAHA OMFROFLBBQ!
Brenda: Yeah. Don't ever say that in public again.
Abby: But LDOS!
Brenda: Last day I ever spend with you....