Frinkle-frock

A classic example:

You are walking down a hall or sidewalk - walking somewhere with a destination. Anyway, you see a person (may or may not be somebody that you know) waving in your direction. Usually, you're first instinct is either :
A) Weird- this person doesn't usually wave to me or
B) I don't know this person.
Either way, you'll be hesitant to wave back- but the wave will either continue or the person will keep looking in your direction. This should be convincing enough for you to wave back immediately noticing that the person was not waving to you at all, but a person behind you. Although the person is unlikely to notice you- it still is somewhat embarrassing. (At which point you may mutter to yourself, ah, frinkle-frock!)