1) When I was young, I lived right by the ocean. It was nice to ride my scooter (purple!) to the coast and back. The neighborhood was quiet with wide streets paved in flat asphalt and it was mostly populated by lower middle class families. One day I was out riding my scooter and right in front of my house I noticed some writing on the sidewalk written in chalk. It said, "Go back chinks". I felt very sorry for my Chinese neighbors to be living in such a hostile environment.
2) I used to take the N Judah home. One time my friend Angie was with me and while we were waiting for the muni a car stopped right next to us at the light. We can't help but look inside and it struck us as odd that the driver was shirtless. Half a second later we realize OH MY GOD HE'S NAKED. Half a second later: "AHHH HAHAHAAHAHAHAHA!!!!" I don't think that was the reaction he was looking for. He peeled off in the middle of our hysterical laughter.
3) During college I worked as a office assistant at the Political Science department. One day a student came in asking about courses. She asked very complicated questions and I had to help her for a long time. She made some odd comments here and there but I didn't think much of it, thinking she's being friendly because I took so much time with her. When she left, my coworker came up to me and whispered, "Oh man, I can't believe she was so obvious about hitting on you!"