As nudist I discovered stinging nettles to be sexually most stimulating.
First I put nettles between my legs and make a nettle crown around my penis.
Second I put nettles between the skin of the hang-tits of my slave nudist friend.
Third I start moving my nettle crown between the slave legs, intensely hitting her skin.
The result is most enjoyable pain while having sex.
Staying naked in the sun afterwards, the exciting sensation is maintained a couple of hours. No marks are left some 6 hours later.