This is indirectly related to Joe's mentor Robert Byrd (see Joe's eulogy at Byrd's funeral in 2010).Therefore, the following was no big deal to Joe in 1985.
It likely didn't bother him at all.
It could be he has a numb conscience and doesn't know what right and wrong is, even back in 1985.
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In 1985 Hearing Joe Biden Says N-Word Out Loud Twice
http://www.youtube.com/watch?v=J5mqIUXppVY