'Guinea' comes up a few times in
The Sopranos, so I'd lean towards regionalism. Here's a clip (
potentially offensive language warning) of Christopher referring to himself as a "skinny guinea'. The other scene I won't post a clip because it involves some minor nudity, but Christopher is having an affair with his cousin's girlfriend who happens to be Jewish. She asks him if he's ever "been with a member of the tribe", and he asks her if she's ever "shagged a skinny guinea".
Regarding 'wop' - I had no idea this was racial slur until I was well into adulthood. One of my mother's staples for a simple, cheap dish that would stretch far and feed many was something we called 'wop dish'. I had never heard the term used outside of that dish. In retrospect, since the dish does contain noodles and tomato sauce, it does seem like a deliberate use of the slur, but nobody in our family knew what the word meant until I shared the meaning of it during a holiday gathering. My aunts and cousins were oblivious to the meaning as well. An uncle by marriage had heard the term, but until then hadn't made the connection between the slur and the dish his wife had been making for thirty some years.
My mother was mortified to discover it was racial slur. To her, it was just another name for a dish, just like 'goulash' was a name for a dish with pasta in it. Both her and my aunts were convinced their mother (from whom they got the recipe) didn't know about it either. Nobody was sure if it was an original recipe of my grandmother's or a collected recipe, but somewhere somebody apparently knew the term to apply it for the dish.
I tend to think it was named elsewhere, just because Italian heritage was virtually non-existent in our part of the US. Everyone was pretty much of German or Scandinavian descent, and to a smaller percentage English and Irish, so pejoratives towards Italians weren't part of the lexicon. Not necessarily out of any moral or ethical righteousness, but the absence of opportunity.
As a kid I loved it, because it had sliced up hot dogs in it. I haven't had it in many years, but I might have to get the recipe from Mom and make it again. Granted, it should probably be renamed, but to be honest, even knowing the true meaning of 'wop', it would be hard to refer to it as anything other than 'wop dish' at this point, after having heard it as such for the first 25 or so years of my life.