Used during a time of aggression when something doesn't go according to plan, not actually as a command.
The abbreviation is generally used so parental figures don't know wtf you're saying.
Person 2: Yeah...FMS.
When you add something to a conversation, which is followed by an awkward silence...
Then you know that you should have kept your mouth shut.
Guy: (oh that fuckin FMS... shouldn't have said that)
A condition where one is always on the lookout for the next cool thing, rather than enjoying what one has, because he/she is "afraid of missing something."