Had a similar issue on the driver's side. There is a rubber button that bumps the glass just aft of center when your window is rolled down. If your window channels are not secure, the glass will bounce off that rubber button and crack. If you don't have the rubber button anymore, you will probably crack the glass just driving it with the windows down.
My doors are pretty rotten, and after three rounds of JB-welding the channels and replacing cracked glass, I had some polymer sheets cut. Slam the door as hard as you like, my door "glass" is unbreakable.
