Would you rather mistook your friend's girlfriend as his elder sister OR would you rather mistook your friend's elder sister as his girlfriend?
First choice, the girlfriend would be extremely annoyed . She'd probably later rant to your friend "Wtheck? Do I look older than u are? Do I really frickin look like ur sis? blabla " She would also lose some of her self confidence for quite sometimes and refuse to walk by your friend's side incase she's mistaken for a sister again.
First she'll be like this,
...then she'll be like this.
Second choice, the sister and your friend would probably feel a bit awkward. And they would go like, " What? No! Thats insane. We're blood related..." But deep inside the sister would probably be all flattered that someone thought she's younger than her age.
Both would go like this...
but later the sis would secretly go like this.
Conclusion, so which one you rather and which one you rather not? It happened to me today and I am emotionally disturbed. HAHA. I would choose I would rather mistook my friend's elder sister as his girlfriend. A reminder from me is that however clueless you are whether it's someone gf or sis always go for the second because it has less consequences ; Like the urge to slap the one who mistook it =P.