You should have a look at the song called 'Jein' by a combo called 'Fettes Brot' (what actually means 'fat bread') from Hamburg. The refrain goes somehow like 'Soll ich's wirklich machen oder lass ich's lieber sein? JEIN!' and the whole song is about wether to take a chance or not. Like that: 'Girlfriend is somewhere else over the weekend. Some other girl you always found sexy asks you to spend the night with her' and then the refrain again: 'Soll ich's wirklich machen oder lass ich's lieber sein? JEIN!'
What I'm driving at is: That song was very big in the charts (Top 10) when it came out in 1996. It went on nearly every pop radio station up and down for a long time all over the country. Nowadays being a DJ and playing that song on a wedding or a birthday party is a sure guarantee to get everybody aged between 8 and 88 on the dancefloor trying to sing along. So I think that word found it's way in nearly everybody's word pool from north to south and east to west and is normally used to get the chance to specify your answer on a yes-or-no question which you don't want or don't can simply answer with 'Ja' or 'Nein'.
That word even has an entry in Wikipedia. And not to forget the Duden entry.