<human>: Could you distill the essence of the text into 1-3 sentences?

Like many other posts here, this happened (6)years ago. 
My school (in Germany) had this exchange every year for the 9th graders with a school in southern France so we could learn french and they could learn german. First me and my class went to France for two weeks and stayed with a student of that french school and after two months they would come and the student we stayed with would stay with us for two weeks. We will call the guy I stayed with Tom.
During the two weeks in France me and Tom became pretty good friends and had a really good time. I had expected it to be awkward but his family was really nice and we got along well from the first day. Since his mother could also speak english(quite rare in France) communicating wasnt a big issue either. 
Note: in France(at least where i went) people of the opposite sex greet each other with a kiss on each cheek(even school kids). 
The two months pass and Tom arrives in Germany and i had forgotten all about the cheek kissing thing. We arrive at my house and my Dad is waiting for us with my little brother and little sister(only 2.5 years younger and looks like my age and very shy). Tom shakes my Dads hand says hi to my little brother and goes over to my sis and starts leaning in slowly to kiss her on the cheek. My sister(not knowing what he is trying to do) leans backwards. He KEEPS LEANING IN. I'm like "wait. wtf is going on?". My teenage mind was way too slow to process what was going on and prevent the awkwardness. When I finally get it I tell him that we dont do that shit here and he quickly backs up and apologised countless times and that he didnt know. He and my sister went red like tomatoes and you could cut the awkwardness with a knife. My brother and parents thought it was hilarious and laughed about it for weeks.
Tom and my sister pretty much avoided each other for the two weeks.
<bot>: I forgot to explain to my french buddy that people dont greet each other the same way in Germany which lead to a very awkward situation.