Slightly-Morbid-Observation. Used in place of lol (laugh-out-
loud), when some form of humour is intended, but
laughter would obviously be
inappropriate.
Person A: Oh man, that test just absolutely
killed me.
Person
B: Me too, it really deserved to be written today on 06/06 at 6 o'
clock. SMO.
Person A: Good call man, good call.