Happened to me yesterday, actually, that a large truck stopped suddenly at the end of an intersection and I, behind them, had to stop in the intersection without knowing when or if we'd move again since I couldn't see anything ahead of the truck. A good seven or so seconds later and the light turned yellow so I had to cut to the right (mostly parking) lane to avoid gridlock. Went ahead a few cars to an opening to get back into a driving lane, cutting ahead a little.

My "I'm sorry" horn is really just my shy hand wave out my window though. I don't use AC nor have tinted windows so I think they generally see how I feel, I think. More often than not, it's a "thank you" horn though, as people often have to let me out of my own driveway since I live on a major street and there is rarely a time there aren't cars idling outside waiting for a light.