Buying sanitary pads shouldn't be embarrassing

But for some reason it is. Not for me anymore though. I don't really care who knows what brand of sanitary pads I buy. The fact is that I'm a woman and I haven't gone through menopause and therefore I menstruate, and everyone who's taken biology knows it. It's no big secret which needs to be kept in the closet. When I was a teenager I found buying sanitary pads incredibly embarrassing, and especially putting the pack of sanitary pads on the conveyer belt at the store. I almost tried to sneak it in between the milk carton and the loaf of bread so that the person behind me wouldn't see it. If the cashier was a man it was sheer torture.
The question is, why is it embarrassing? Is it because we don't want any guy to be reminded of the fact that we bleed from our vagina once a month? Everyone above the age of 10 knows about it but yet it's something that's best kept quiet. Is that why they always use blue ink in the sanitary pad commercials? Nobody likes the sight of blood, or even the thought of it. Or more specifically, nobody likes blood that emerges from that particular area. Why is that? Is it because those areas are very private and intimate?
Men don't like buying sanitary pads for us either. It makes them uncomfortable. They can buy condoms without any hesitation, but sanitary pads is a whole different ball game, even though condoms are just as private as sanitary pads. They end up in the same general area. Is it because condoms say "I'm gettin' some!" and sanitary pads say "I'm whipped, my wife/girlfriend/fianceé has me buying her sanitary pads!"?
My father is the expection. When I was growing up he bought sanitary pads for both my mother and I without feeling ashamed. This is probably due to the fact that he doesn't really care what people think of him. My common-law dislikes buying my sanitary pads. He will do it, he just doesn't like it. When I asked him why feels this way he couldn't give me an answer, he just said he simply doesn't like it. It's almost as if men don't want to come anywhere near those products, even when they are still in their package and haven't even been used.

Another thing that's embarrassing but that shouldn't be is when we slip and fall in public. When I slip and fall, my first thought is not about the pain but about whether or not I was witnessed falling. At the moment it's happening it is worse to be seen falling than to get hurt in the process. Why is that? Why do we put our egos ahead of our personal comfort?
It doesn't help that some people actually laugh at other people falling on their ass. This mystifies me, since I fail to see what could possibly be amusing about that. If I was 5 years old I might find it funny, but I think my sense of humour has evolved since then.