A syndrome in which the said subject has trouble deciphering which thoughts to express aloud, and which to keep silent.
Often the source of embarrassment of subject's companions.
Kyle - Chad has SFD.
Bailey - You reckon so?
Kyle - Yes, he just asked me if I would graffiti the school's walls with him while we were eating thanksgiving dinner at my grandma's house!
Bailey - Yeah... he does have difficulty gauging what to and not to say.
Chad - (rather loudly) GUYS I'M SO DRUNK!!!
Krystan - Chad! Stop being to SFD! I'm on the phone with my mother!!
Chad - I really need to take a shit.
Teacher - ... SFD...