Here's an article on Slate about summer fashion faux-pas. I couldn't have said it better myself! Just because it's summer (or anytime of the year for that matter), it doesn't mean that we should abandon fashion common sense. I particularly enjoyed the author's description of bad sandal etiquette:
But if you are a man who chooses to wear sandals, be aware that the person staring at the ground may actually be glaring at your feet.
As for flip-flops, the sandal's plastic cousin, these are office-appropriate only if your co-workers don't mind that you sound like a metronome as you walk.
I'm glad to know that my fear of summer sandal feet is not unfound.