In Bulgaria, shaking your head means 'yes'.
In Bulgaria, a sideways head shake traditionally means 'yes' and a nod means 'no', the exact opposite of most of Europe. A similar custom exists in southern Albania. Because many young Bulgarians switch to the Western version around foreigners, confusion doubles: you don't know which system the other person is using.
Useful: When in doubt, ask out loud: 'da' means yes, 'ne' means no.
Source: en.wikipedia.org