Well they wanted to kick my *** because i was black.
I don't know what my response would have been in all honesty. I can tell you for sure that i would have felt singled out because of the color of my skin. Again, without knowing the kid's intention i really can't say one way or the other.
If it was someone I know like a friend and the comment was directed at me personally, i would have thought it was funny. My friends and I joke about each others race/ethnicity, religion, nationality, etc.. all the time and we have a great time with it. But we know each other very well, we respect each other a lot and it is understood that its ok and it is always done in good taste and humor.
If the kid had said "all old people leave the store", it would have been considered rude and disrespectful.
No matter how people want to define 'racism', when you single out a single group based on race, it is racist. But to be able to discriminate you have to be in a position to withhold access to something (i.e., resources, opportunities, etc...) from a group based on race.