Say it ain't so, Joe

[Geggy]

Can anyone tell me what does it mean when some people say "I ain't got no job." If the person does not have no job, does this mean they do have a job? Does no times two in one statement means they do have a job? What about "I didn't do nothing"? Did the person really do something when they say they didn't do nothing?

like for example,
'hey i don't do nothing.'
'oh, yeah? what do you do?'
'I ain't working at no IBM corporation.'
'Wow, IBM, huh? well, cheers.'