I'm just posting this anecdotally, not as an endorsement or anything, but years ago I was reading a similar thread on another bike forum, and a guy said he was having serious problems with some jerk in a car. So at some point he caught up with the guy at an intersection, and as he was slowly riding by, he hammer-fisted the guys windshield, and busted it ! He said that there are two 'sweet spots', or weak points on a windshield, (at the 1/3 points) where a hard blow can break the window.
I've never tested this myself, but I did commit it to memory !
