How does this work?

I put my car up on a lift at school today so that all of us in class could look at the suspension since we're learning about it, and so that my teacher could look at the power steering setup.  While we were all standing around it one of the gentlemen was leaning against my car.  My quote was "Boy, get your hands off my car!"  Now, I'm a humor filled, sarcastic person and that phrase coming from me is obviously just my humorous, sarcastic way of saying, "Dude, don't lean on my car."  I thought this was an easier, less jerkish way of saying that so I jokingly said it.  Apparently the word "Boy" used in that context is degrading to some people.  Well, anyone who knows me knows I am in no way racist and in every way sarcastic, so no one I know would take offense to me being an idiot, but this guy was livid.  My teacher explained that the term was degrading to him and I simply said that it didn't make sense.  I mean he is a boy, as I understand it, so I don't see how calling someone who is a boy, a boy, is degrading.  I'm told it's almost like using the N word though.  Now I apologize for offending the guy, and I'll be sure that he knows it was meant to be all in good fun tomorrow after I'm cooled off a bit.  He also proceeded to say that had be been his younger self he would have clocked me.  That's what really set me off, and so I told him that when it was his $26,000 car that he was leaning against I wouldn't say a word.  I just want it to be known that I would have used the exact same phrase had it been anyone else leaning on my car, and had it been a girl, substitute that in for "boy."  I mean honestly we're all grown and in college, if you can't take some sarcasm by now you need to lighten up.  And most importantly, don't lean on my daggum car!  We've ALL been told that by our teacher!   I wouldn't want to pay for a new paint job on a brand new car that's for sure.