I am a fangirl. I admit it. I love a Korean pop group called EXO to the ends of the Earth, and I went to one of their concerts this year -- it was amazing. As a fangirl, it is fun to talk to other fangirls about favorite members, songs, and performances and to appreciate K-pop groups together, but as a fangirl, it is not fun to learn of extreme fangirls who tarnish the credibility of entire fandoms with their actions.
It's OK have posters of the groups in your room. It's OK to make clubs and organizations with and for fellow fangirls to help enjoy K-pop (or other things, like TV shows, actors, musicals, books, etc...). It's OK to see them in concert and take pictures with your favorite members. It is not OK to embarrass, stalk, or physically harm anyone in the midst of fangirling.
You know the type. These fangirls are the ones who believe that getting close to their idols by any means necessary is OK because in the end they will both fall in love, get married, and live happily ever after.
It doesn't matter if they can be sued for kidnapping if they can trick their favorite K-pop group into entering their fake band van. They can just drive off with their lovelies, and nothing will be wrong, especially after the idols realize that their van driver is an unfamiliar teenage girl.
It doesn't matter if they have to slap their favorite idol in the face if they can engrave their presence into his mind forever. He will never forget.
It doesn't matter if they scare and burden their idols by sleeping in front of their homes and trying to guess the password to their locks. They will succeed and get in one day.
These fangirls are terrifying in their resolve to ignore ethics and respect just to get what they want. If you are one of them, please ask yourself: Is it actual fangirling, if you are hurting the idol you worship? I don't think so. Sasaengs refer to the extreme fangirls, and to a Super Junior member, Heechul, they shouldn't even be called fans. I agree. It's a case of people going so far in one end of a spectrum that they flip the spectrum and end up on the other side.
Sometimes, fangirls forget that idols, celebrities, and everyone else love their fans a lot. They work hard to make the fans happy with new songs or new shows and always make sure to thank their fans for their support. Don't take away that gratitude and love from them by stepping on their privacy and disrespecting them. These idols and celebrities are normal people who need space to live their lives.