I just read the story 'How I Became a Masturbation Addict'. Wonderful story by the way, one of the best I've read here. The author describes going out in public wearing nothing but a long coat. I have done the same thing, both on streets and in rural park. I have a very lightweight coat which is ideal for summers, and a mid-weight raincoat which works well in fall. I like the lightweight coat best because I like to think my body shows through a little.
I have put either rubber bands or a set of my nipple lassos on my nips before going out in a town (briefly, in a store or a mall). The nipple lassos work better, and are easier to apply. My nipples stay amazingly erect that way, with no stimluation other than the gentle rubbing against the fabric of the coat. I have had both men and women eye me appreciatively when I'm walking or standing in a store this way.
I've also detached the inner edge of the side pocket of the coat, so my good left hand can reach down and provide much-needed stimulation between my legs. Obviously I can't just walk around stimulating (wish I could), but it's perfectly safe to turn toward a store window or a display counter for a few seconds, let the left hand inside, and give several delicious rubs. I have come very close to cumming in public this way.
Another thing which is extremely sexy to do, is what I call 'flashing the wall'. I can turn toward a wall or a tall display shelf, open the coat momentarily exposing my whole naked body. I have never actually masturbated while doing this maneuver, but I don't need to. Just the act of being completely naked in public is erotic enough.
Of course, in the car or on a park bench, I can open the coat, spread my thighs, and masturbate with abandon. In the car, I'm very careful not to cum while driving (well, I never cum on purpose while driving...) but on a park bench it's heavenly to reach a complete and excellent orgasm, one which sometimes goes on and on. There is simply no other sensation quite like it.
This may be one of the advantages women have over men. There's no huge erection sticking out to betray us. Erect nipples have become so common that it's completely acceptable to walk around with your nips sticking out, yet it still feels very sexy. A fully erect clit is probably just as enjoyable as a fully erect penis, and with occasional manual stimulation the clit can stay that way for hours at a time.
For those who haven't tried it and who are inclined toward exhibitionism, I highly recommend this 'naked coat technique'. Don't forget to detach one of the side pockets of your coat-you're really missing one of the ultimate, salacious, exotic sensations if you don't do that.