Jmat said, "People consider it a sign that a person is uneducated."
Unless you are south of the Mason/Dixon line of the U.S. 'Ain't' is slang.
In southern states, 'ain't' is used as an emphatic expression, "I ain't going wash the dishes" or " She ain't pretty at all."
On the northeast coast or the west coast, 'ain't' is considered uneducated because it is commonly used in southern states. These coastal regions are bigoted or hateful toward people from southern states. Thus, anything common in southern states is viewed negatively in the east or west coast regions.