If you're not going into the physical details, I guess I might need a bit more clarification as to what you feel you cannot say and why? We may be running into a cultural difference or social stigma that I'm missing. If I want to flesh out a philosophical point about myself in relation to BDSM without regaling my listener with details of my last flogging, I simply describe it along the lines of, "I prefer a man to take the lead in the relationship," or, "I enjoy men with a dominant personality, it allows me to let them take the lead and relax into taking care of them."
I've "slipped" like that before and, sure, there have been some raised eyebrows, but I don't recall any animosity which is good. Perhaps that's why it doesn't bother me. If people seem especially interested, I've always just smiled and said, "well he has to have a name special to him, and 'Sir' is certainly nothing I'd call anyone else!" or something like that. I also use the term playfully and with a smile around folks we know so it doesn't seem odd or forced when they do hear it, an thus it isn't something strange to them or cause for worry.