May happen after a frape (a couple of my male mates now say they are married on facebook as they do act like a married couple sometimes, after someone set it without them knowing as a joke, they just left it as they are not in relationships or anything and its pretty funny as we all call them an old married couple even though they are both straight), or may be to hide the fact that they have recently broken up from a partner and dont want those messages popping up to say soandso is recently single or whatever… with the family thing I have found with my mates it happens with the people who arent so close to their own family or really really close to their mates and so will call their mates their family. Other than that it is a little weird and I dont do it but each to their own hey!