I am a 15 year old boy

That's right. Periods scare the hell out of me. I am extremely uncomfortable with the entire idea of Menstration. I myself have not had one in close to two years; as soon as I started birth control (for debilitating cramps, ironically enough) I was like "I can opt out of this?!" and haven't looked back since. The advantage that most 15 year old boys have that I don't is that generally strangers don't approach them in the bathroom, asking if they have Midol. And I would bet that when hanging out with their buddies, they never talk about cramps and white pants and bloating. I envy them. It was worst for me when I was on swim team, almost every day someone was trying to bum tampons. When you live in dorms all the girls just assume that everyone wants to know when they are PMSing or whatever. And yet I don't know of any tactful way to tell people, "What the fuck is the matter with you? Periods are not conversation fodder and I don't want to discuss any aspect of them with anyone, ever!" My 11 year old little sister started hers last year. She was 10 years old. I have no idea how old I was because I didn't tell a soul. I just took care of it and never mentioned it, the way every female should. My parents finally confronted me when I was about 16 and traumatized the shit out of me with "the talk."
Anecdote:
My other little sister once asked me to take her to the store so she could pick some stuff up. Whatever, so I drive her there and as we're getting out of the car I ask what she needs to get.
Chapstick, YM magazine and some pads. WHAT?! I get back in the car. She's banging on the window, you know, "What's the matter with you, come on blah blah" and so I roll down the window and shout "I'm not going in there with you to get," whisper, "pads!" Yes, this is me, the sophomore in College with my 14 year old little sister. I don't care. Periods are scarey. Period.