I wear them because they're prescription and I wouldn't be able to see well otherwise.
Also, you can't tell(because I'm wearing sunglasses), but I'm observing you on the starting line glancing over at me with disdain in your eyes.
Though I also see something else...
You are unfocused and afraid. You try to mask your uneasiness with an apathetic look but your demeanor and posture betray you, and I can see it there clear as day.
Lashing out in anger against your inner fear, you mutter to yourself "What a tool." "That dude looks like a total douchebag with those glasses." "What a f*cking fa-" UH OH, you got caught staring. The subtle smirk on my lips causes you to immediately snap your head forward as your face turns a notable shade of red. Part anger, mostly embarrassment.
You've lost your edge. You are now completely unsure of yourself and hesitant. I am now amused and confident. You shrink inside to the pathetic, jealous, anxious little twerp you've always been. I on the other hand embrace the judgement. I am the Alpha Male. I am the Predator. I am everything you wish you could be. And my smirk will grow larger as I destroy your feeble, weak, emaciated body in the final stretch of our 19-minute 5k.