I once spent a ridiculous amount of money to spend a day in a luxury bathhouse in Europe (basically, a swimpark for adults). When I made it to the pool I was looking forward to most, there was a couple having sex in it. Loud sex. Ugly sex.
Of course, I couldn't use it after that.
There where kids just around the corner, too. There weren't any doors between them and us. The kids were being loud. A kid could have walked in instead of me.
So, stuff like stroking him and so forth is fine, as is having sex in a secluded area of a park or even a restroom, but if its somewhere where you can be seen, it can be annoying and offputting to others.