Here are a few things I, personally, have done, would do again, or been thinking about doing for awhile:
There are many adult parties of all kinds going on in San Francisco. Most of them private but do post their information on a few sites. They range from "Eyes Wide Shut" where you have to be a part of a certain circle, to a few parties organized by escorts, to several low-key but still high-end house parties, to just plain "down and dirty" orgies that will accept just about anybody. I'm not a part of any "elite only" circle but can give you information about all other action in town.
One of my favorite and sexiest bars in town is Redwood Room at the Clift hotel. It's set up as a very nice and spacious lounge with very high ceilings and unique decor. Generally, great looking crowd, good music, and delicious but pricey drinks. I'd recommend making a reservation if you want to sit. For experienced and observant: extra points if you can spot working girls there. If you are feeling adventurous, perhaps take one to your room? (Just naughty thoughts
Another romantic spot is Yoshi's - always great live music, mostly jazz, 40+ crowd. They have two locations: San Francisco and Oakland.
For a walk on a wild side, I've been thinking to do a quick naked photoshoot. The type where you wear a long coat but nothing underneath. Arrive to one of the awesome SF areas, drop the coat, and shoot! Sunrise time is best in terms of lighting and less of a crowd. Since this city is one of the most liberal in the country, you are unlikely to get in trouble.
And last but not least, if you really want to be kinky, you can engage in some public or semi-public sex (just make sure kids or places with kids are nowhere near). Best places I've tried that lower your chance of being arrested are: your car, a parking lot after dark, stairwells, and any other objects and structures that provide a cover especially where you can see public much better than they can see you.
Happy exploring!