Hahaha, I've joked about the exact same thing. A tank would make intra-city commutes all the more merrier, amusing, and pleasant, even if it would be loud. 

I've also joked about wanting a bazooka. *That* would stop a would-be thief their tracks, if they're suddenly concerned about having a mortar launched at them.

I remember teaching my daughter to drive. She was driving us home one particular evening and let out a series of curses at the driver in front of us whilst questioning his parentage, lineage, ancestry, and future in the gene pool. At that moment I realised she was absolutely ready to drive on her own.