Use electro razor, while squatting over a small mirror. Use baby powder to make it easier. Using a razor will cause a lot of irritation! I use this one, it'a a bit pricy, but it works like a champ, the cheaper one, snags hair and can cut you...

You could try the Philips (Norelco) Bodygroom.

Well, how did you remove the hair on your crotch? I'm guessing that you shaved it. So shave your ass.

'Sorry, I guess that was a kind of flippant answer. Yes, I know from personal experience that shaving your own ass isn't easy. Therefore if you like being hairless and want to be so permanently, consider laser hair removal. I had it done, front and back, about ten years ago and I love it.

You're a really hairy guy, so you'd probably at least four or five sessions (maybe more) for complete removal. I had three on my crotch, two on my underarms and one on my chest.

But please, please, please don't even consider removing your heavenly leg hair. The thick, black hair on your legs is spectacular. You'd be super hot with hairy legs but completely hairless everywhere else. And if you had a black beard, that would be even better.
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How 'bout some photos of your ass? Maybe leaning forward so your cheeks are spread and we can get a good look at your hairy crack and your treasure hole.