PSA: Commonly used acronym by Nigerian men. Ladies/Gents, keep your eyes and ears wide open; when you hear a man say/txt/msg/whatever is yet to come "SMDH", RUN AS FAST AS Olusoji Adetokunbo Fasuba! They are most probably going to hurt you, break you, and turn you into an emotional wreck, CHINEKEMEEEEE!
EXAMPLE :
if a guy/Nigerian guy says "SMDH", proceed speaking to him with caution, he is most likely a Nigerian Demon AKA EXTRATERRESTIAL Fuckboy)
Internet abbreviation. Used to refer to the act of shaking ones dickhead ("shaking my dickhead").
May also be used in a metaphoric way, e.g. you consider something as that nonsensical and unacceptable that "shaking my head" would seem understated or too posh.
literal example:
A: man, I have no toilet paper B: just shake your dickhead
A: okay I am smdh
metaphoric example:
A: dude, my city council decided to build a sewage treatment plantin the middle of the old town
B: smdh