My parents named me Sebastian i like my name but its to long so i need a nickname?

We named our son Sebastian and one of my old friends told me the best nick name I've ever heard for that name. He said in High School they had a foreign exchange student who's name was Sebastion and the actual nickname in Germany is "Basti" pronounced "Boss-tee" It is actually the middle part of the name (take the SE off the beginning and AN off the end) anyways we call our son Basti and I think it's a pretty bad Azz sounding nick name.....and if anyone asks you about it u can tell them it's the ACTUAL nick name for Sebastion....just like John is short for Johnathan or whatever.

My name is Sebastian, I'm swedish and popular nicknames for Sebastian over here are Sebbe or Basse. I know the former is hard to pronounce for English speakers. Other more English friendly nicks I've been called are, Sebbie (more childish) and Seb