Well! First of all answering like this, FOff i mean isn't nice and it's positively not something u want to tell your either boss or a girlfriend, or anybody relationship with whom you value, that's kinda rude and mean, but sometimes it may be the only way to let somebody know they are not welcome... a lot, and sure the F word is bad, but F off does nothing with sexual activities))) it's like "get lost" nd I guess the latter would be better, the same meaning but without obscene lexics