Missing self-confidence or just discretion??

This will be only a written form of my thoughts. I realized that i have a big problem with the public photography.

Basically this would be a simple situation. I grab my camera, go out, and shoot pictures. Right? Not a big deal.

BUT. My personal (and as i see this is the usual) feelings about being a subject of a photo is not really positive.

I identify 4 kinds of people. The first one (like me) hates to see himself on a photo. Hates the situation to know that he-she is recorded by someone. Usually those are who raise their hands to cover their face, or looking straight to the camera with an evil look. The second one who does not care. They are the subject of the most urban pictures. You can see them on every picture. The one, who is walking-standing-sitting naturally. The third category the ones, who come to you and ask if he-she can see or get the picture about him-her. (They will stop for you, and will nod for you if you smile to them). The last category (and if possible the worst one) who wants to be on all pictures. (usually appearing on events - like concerts, parties etc.) and chasing you. asking. please take a photo about me and my friend, girlfriend, dog, beer, hat, whatsoever.

But. What if i'm walking in a park, and i see a couple sitting on a park-bench, looking into each other's eye holding hands, and smiling with the most amazing 'I'm in love with you' kind of smile... If i try to ask for their permission, the moment will break. If i didn't that would be rude. If i didn't and than go to them to show and ask for their approval to keep (and send) the picture for them could work, but what if i have to delete a beautiful picture?

I know the solution is just to do it. Without doubts. Any idea how to handle these situations? :)