I remember as a kid I locked the door to the car whenever someone would walk by. Most people don't really notice or care but once a black guy walked by and I didn't know about the racist connotation, so I just did what I always did and was devastated when I could see that I really hurt the guy's feelings. I stopped doing it after that, now I just give a little friendly wave or smile. I'm still as overly cautious, but I'd rather get stabbed to death than make someone feel like that ever again.