Checking out random guy's junk?

For the past couple of weeks, I've been checking out guy's junk. I don't know why, but I catch my self just staring at it when they walk or when they're just standing there. I'll be doing it to random guys who I've never met before! Girls, have you ever had this problem? And guys, do you notice if a girls (or has been) staring down there? What does it mean?

For example, I was sitting at the cash register and this 17 year old guy who I kind of know, was walking towards me with a bottle of pop, and he was carrying it normal, but I was just staring at him down there. I hope he didn't notice.
Checking out random guy's junk?
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