I dressed up as Mr. T in University. I didn't even consider the racist implications of it until I got to school and remembered two of my profs were black and born outside of North America. One stopped class to ask me what I was dressed as. She had no idea who Mr. T was
I also had one black student passerby in Mac Hall give me the dirtiest look ever. I felt like a bit of a dink, as I hadn't even considered I'd offend people. I'd probably wear it to a party where you know most people, but doing something highly public will probably lead to someone being offended.