socially awkward boy magnet?

Does any one else share this problem. Today at the grocery store I walked in and caught the eye of one such boy-gave the necessary courtesy half smile and quickly walked on. This boy followed my through my entire shopping trip. I kept trying to dodge him and he kept reappearing in the corner of my eye. He finally caught me with my guard down long enough to approach and awkwardly introduce himself and ask if I wanted to go for coffee sometime? HUH? He probably doesn't even drink coffee and just thinks this is the protocal for getting a date. To say the least I quickly turned him down (as gracefully as can be expected). Eeek! This seems to be happening a lot to me lately and I'm beginning to wonder what kind of vibes I'm giving off. Where are the normal boys. help me.......