Awesome thread... I have one.
My family, when I was about 15-16, hosted an exchange student at our house for a couple of weeks. Now, normally, this program would have worked as a direct exchange (in this case, I would have gone to her country for a couple of weeks with other kids from my school and stayed with her family, and then she and her schoolmates would come here), but her "exchange partner" declined to participate in this side of the program. Instead of seeing that for the warning it was, I got really excited about hosting this virtual stranger! Kudos to my parents for being gracious enough to extend the invitation, but cautious enough to keep a close eye on things.
The student, who I will call C here, was an... interesting girl. Interesting not because of her different culture or anything... but she was an SS in her own right. Her schoolmates really wouldn't have anything to do with her, and I quickly realized why.
-she would not eat. No, strike that, she would not eat ANYTHING that she had not brought with her from her country. After a few days this dwindled down to random chocolate. No, she would also not offer anything to anyone else. She refused my parent's cooking by literally saying, "that is absolutely disgusting". My parents are nice, but they are not pushovers. One alternative or sidedish was offered each meal, then she was on her own.
-one part of the program was to go to a local amusement park for the day. She insisted on riding one rollercoaster many many times. Well, with the above diet, you can imagine how that went. She threw up all over the platform, and then wanted to ride again. The staff made her leave, and we sat together outside of the ride as she flat out refused to do anything else.
-She loved to take pictures of our dogs. Fair enough, they're awfully cute. But god help you if my family or I happened to be anywhere near the picture. She would actually tell us to get out of the way, and in a very blunt manner - this happened every time.
-We got a new car while she was here. New to us, at least. When we all went out to see it, she sniffed, put her nose up (I had no idea people actually did this as a serious gesture of disdain!) and said something like, "the only good cars are Audis."
-She went to visit family members while staying with us, which was not only fine, but welcome at this point. Her family members lived about 2 hours by train away from us, and the deal was that she would leave on Friday, and return on Monday. She came back on Saturday afternoon with no explanation. My mom thought that was kind of funny, but pretty indicative of her personality.
-apparently, she treated me really poorly throughout the trip, but I must have blocked this from my memory. My mom, years late, would shake with anger when talking about how she would insult and put me down IN FRONT OF MY FAMILY. Who does that?
For the entire time she was with us, she barely spoke, and was just miserable to be around. From what I understood from the other students, that was pretty normal for her. Why would someone put themselves into that kind of program if they have decided not to enjoy it?
My mom ended up driving her to the airport to go home, and she actually asked about coming back to visit. From reading between the lines, I believe that my mom outlined to her exactly why that would not be possible. I think my mom also might have called her parents and read them the riot act about her behaviour.