I had a female friend and she had an old sun lamp which one night we set up in her bedroom and I turned it on. I stripped to my pants and sat cross legged in front of it with a blindfold to shield my eyes. When I turned round 5 minutes later my friend sais I would get a tan line and maybe I should remove my underwear as well. I slipped them off and lay on my front, naked with my arse getting the full glare of the lamp. When I turned over 5 minutes later to sit with my legs apart, the lamp shone on my now rock hard erection. Even with the blindford on I could sense her eyes looking at my manhood. I never touched it but enjoyed the feeling of sitting there naked with my erection pointing to the ceiling. She never said a word about it, just stared. When I had finished, I stood up and she offered to rub in a cream she had, so I lay on top of her bed while she gently rubbed in the cream and when she got to my penis she said 'would you like me to play with it'? Her tugging and pulling was rough so i showed her how I liked it to be done.
From that night on, whenevr I stayed at hers, we would share her bed and I would lay naked while she wanked me off. She remained a friend only but would let me walk around nude in front of her without a mention. I never fancied her sexually but being naked in front of someone is the biggest turn on for me I can think of.