Rimming. Annilingus. Putting your tongue where the sun don't (usually) shine. Something that I had no idea I would like, both giving and receiving.
With this particular kink cleanliness, obviously, has to be thorough. But once that hole is as clean as can be then all sorts of new sensations can be had.
When giving it takes intimacy to a whole new level. My partner has opened and given themselves to me completely and I love the feel of that taut pink ring beneath my tongue.
I only experienced receiving recently and, perhaps surprisingly, it was when I was topping someone. This particular sub, when allowed, liked to put her hands and fingers everywhere and so I had prepared with both soap and razor accordingly.
Straddling her to get a better position for my mouth on her clit she started sucking my cock. Then she lapped at my balls. Then her slathering tongue sought out my arse. And it felt really very strange. Wet. Soft. Warm then cold.
It felt good. It's a hugely sensitive part of the body for me and I'm sure the same is true for many other men. Briefly she had control, but that was because I was giving her control. Another situation and I could have enjoyed that all night long. Maybe one day I'll let it happen again.