In the past lots of people lived on the country side - villages. All days they were looking after their beloved - sheep. As time were passing, cities were built and people from villages started to come to the cities. Some of them started to behave appropriately to the new living circumstances, some didn't. They still think they live in village and watch their sheep. Therefore we call them chobans.
E.g. Ivan comes to the city from country side. He likes sheep. He is choban.
Choban is sheep guardian. In past, dull and rude boys were chobans. They lived in mountains and come to villages only few times a year. Today, we have many people with social and intelectual skills of choban, so we use that word often.
Ivan je choban.
Ivan is dull, stupid and don't know how to behave properly.