It depends on the laws in that particular country
I'm UK, so have no idea what your laws are
in the car at night or a really deserted stretch of road, or at home or digs - absolutely no where else
My ladyfriend and I have had sex in public in many places (restaurants, ferries, on top of the Rockefeller Tower in NYC, on top of the car alongside the I5 in California, against a tree in a public park in Toronto) — the trick is to appear as natural and relaxed as possible and 99% of the people will not notice you are fucking in public. It's some of the hottest sex imaginable.
Big-haired Bitch/Personality Hire
It's outlawed in most places publicly. Period. Especially if kids are present.
Your best bet would be somewhere dark and secluded, like a bar or a restaurant with mood lighting. Somewhere that you can be discrete but still have that thrill of being out in the open.
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legal matters only matter if your caught, so just be sneaky. The risk could be a turn on.