When you've entered, are about to exit or are cruising through the parking lot of an establishment looking for a parking space, and you stop for a pedestrian crossing to or from the parking slots (unlike so many other drivers seem to do these days) and you politely wave them through so they know you'll wait, and the pedestrian not only does *not* acknowledge the fact that you did so, but also proceeds to walk sloooooooooowly across your path*...almost as if they're doing it on purpose as a power trip. I really hate that. I do wish politeness/graciousness could be met with equal measures of same.
*This in no way applies to the visibly disabled or infirm. I'm talking about people who were walking just fine a split second before you stopped for them.
The reverse just happened the other day. I was leaving the grocery store, and stopped for a middle aged gentleman to cross in front of my path. I waved him through, and he waved back and expedited his trip across my path - it was unexpected but very appreciated. Just a nice gesture from one person to the other, as if to say "thank you for politely waiting for me to cross (as you should, since, hey, you're in a car and I'm not) and in return, I acknowledge you're waiting and will make a small, but noticable effort nonetheless, to be equally gracious to you." It was very nice.