On holiday in France once, while trying to chat up some French dudes, my friend whispered to me, “How many blackbirds were in the pie?”
I can’t remember what she was trying to work out but I guess it was something to do with the number 80 because the rhyme is ‘four and twenty blackbirds baked in a pie’, which is like ‘quatre-vingt’, which is 80.
I never got to find out because I spent the next hour in hysterics (the French guys left).
Yeah, that´s another thing only we do I think. We have that in common with the chinese, only for them it´s more official. 
This actually happened:
I was standing in a french bakery with a friend who didn´t have french at school. He´s trying to order something, leans over to me and whispers in my ear:
“Hey Milan, what´s the french word for ´Baguette´?”
I basically haven´t stopped laughing at that for the past 16 years.
This is not only common in Bavaria but in most southern regions of Germany, for example in the Saarland. Among friends it is common in northern Germany to use only the last name like “der Fahrnholz” - but this is mostly used instead of a nickname.
We had a number of fellow students at school who were refered to only by their second name. No one knows who decides that, it just happens. I was never one of those, though.