I know it is a bad habit and you hate it, but smokers are being considerate of you by following the rules and smoking only in the designated smoking areas. Please try to be just as considerate to smokers by NOT camping out in a DSA because of it's shade or seating. There are plenty of places to sit at the parks but very few DSA's. And please don't complain about the smoke if you are in a DSA.
If only that were true, 
I did, as I'm not one to willingly throw someone into an asthmatic fit (or whatever her condition was), but did find it incredibly odd that she willingly sat in a DSA and then asked all those around her to move.