Well, I'll try once more and then if it's still beyond you, well, there are more things in heaven and earth, DappledThings, than are dreamt of in your philosophy.
Some people like to dress as Goths because to them, it feels a bit rebellious and alternative and outside the norm. I'm not one of them; I don't really like the Goth aesthetic, don't really "get" it, if you will, and don't think it's very rebellious to wear black and listen to Joy Division. It doesn't seem like much of a big deal to me. (And yes, I know some people are Goths because they just like it. I'm just trying to form an analogy here for the perpetually and not at all performatively confused.)
But I understand that to some people, it does feel a bit edgy and it scratches an itch in them. I find this very, very easy to understand, actually. It isn't puzzling or bemusing or difficult at all. I definitely don't go to Goth forums so I can tell them, after a day and a night of discussion and explanation, how I just don't understaaaaaaand why they're Goths. I also understand that it doesn't actually matter if I don't understand.
So while the dirty burger may seem unimpressive to you, to some people it just feels a bit naughty, and they enjoy a small secret thing that's just theirs. That's it. That's all. You can substitute it with "secret spa trip" or "secret wank" or anything else; the concept maps over.
I really can't think of any simpler way to put it. If you still don't understand, well, it doesn't actually matter. You don't understand it so, with respect, there's no reason anyone should care what you think about it. Go, be free, join a discussion about something that interests you and that you can follow. I can help no further.
The kicker in all this? I actually hate McDonald's.