There is really no way to avoid offensiveness in jokes. People just need to learn to not be so easily offended. I'm guessing that that joke would probably be offensive to South Africans.
Banknorth Garden has a below-ground parking garage on the premises. That'll probably be your best bet, but I'd park as close to the entrance as possible, because traffic coming out of there is insane after an event. Good luck, and have fun!