My brother, when we were still single. He's the only one I've ever talked openly with about it. My step-sister talked with me about her vigorous sex life occasionally, and that was so horny, but would never mention masturbation.
In this forum, we can talk about it with each other openly and share our experiences without any inhibitions.
I have a few male friends I've discussed masturbation with but not in details. However, my current partner and I talk about it. Our first night together she asked me questions about how often I masturbated and told me about her toys. Our second time together, she told me she was so turned on after our (sexless) date that she had several orgasms from her dildo and vibrator. Those initial conversations paved the way for us to talk openly about our sexual desires and ask for what we wanted.
Mostly strangers, but I have two friends, who are an exception. One I used to masturbate with, so it is pretty natural, though we also don't talk about it often. And another friend whom I have never been sexual with, but we talk about sexual encounters and experiences from time to time, wanking included.