@MrGozaemon No, it's not even slang exactly. It's a commonly used incorrect term. It's often attributed with uneducated individuals. You should know what it means, but it's not something worth adding to your vocabulary.
@MrGozaemon You wouldn't say it with your friends unless you were from a culture that uses this word often. It is considered uneducated, and will mark you as ignorant of standard English. The dictionary contains many non-standard and slang terms, but that doesn't mean that you should use them.
@MetRon Most people use "ain't" in the south and it doesn't mean they are uneducated! Most people know the correct use who use it; it's just the way southerners are used to communicating with each other! There shouldn't be so many negative stereotypes.
@ceraunavolta I was born and raised in the south, and I don't say ain't, unless I am singing along to a country song. Still, I don't use it in conversation, and neither do my friends. It isn't a negative stereotype, it is just wrong.