Well, I do keep a spring loaded center punch handy and strategically located on the bike. It's for those occasions when a cager starts getting silly and needs a wake up call.
I kick doors and dent the hell out of them when I'm wearing steel toe boots, but I don't always ride wearing them.
The center punch easily shatters windows by just "touching" them. Most of the time they don't even realize that I did it, works great.