An abbreviation for "Fuck Me Dead", a common Australian expression for amazement and/or bewilderment.
FMD you are a dipshit.
Fuck me daddy
Ohh god FMD
Fuck me daddy A very popular phrase lately, no need to explain
'Omg ur crush is going this way!' Me: 'OMG STFU HES SO HOT FMD
FUCK MY DAD
Oh FMD