That's the point. If we allow reverse harems and all other types of harems, as long as there is a main person being liked by a bunch of other people, then the OP's sister should also agree that if a bunch of girls like a single gay guy, then it is considered a harem. Since she believes this actually does happen in real life, then harems can exist in real life.
@AURON570:It just occurred to me that OP's sister said that harems would not work in real life because even if a bunch of girls liked a guy, the guy would either be gay or turn gay. But wouldn't this still be considered a harem even if the guy is gay? or even bisexual or a hermaphrodite? Or does the guy HAVE to be straight and/or fertile?
What about reverse Harems?
Hmm I suppose. I guess we're left to question what qualifies as a harem and whether it is practical. I don't really think it's practical these days for either the girls or the guy, to many factors to consider. But I guess it's possible, even if it's just role playing or whatever. But then it still will never be like the ideal harems in anime obviously.
Harems does exist in real life, Kings in the old days have them (but not in the same way as anime show them)
Thats what I was thiinking a real-life Harem can happen if you got alot of cash.
" @AURON570: Woah woah woah you dropped To Aru Kagaku no Railgun? I guess if you watched it on its own (without watching what it's a spin-off of , To Aru Majutsu no Index) it'd be really difficult to get into at first, but there are some really awesome arcs later on in the series. I'd also understand if Kuroko turned you off from the series, since her obsession over Misaka is something that takes a lot to get used to. 'xD "yeah, that's pretty much what happened... I forget how I heard about Railgun, but I thought I'd give it a try, not knowing it had a parent story. I couldn't really get into it, I guess it's just not for me. I'm thinking about giving it another shot by starting over from Index, sometime in the... vaguely distant future. =S