This self-defence jacket from No Contact gives any creep who tries to grab you 80,000 volts of low amperage electric current pulses (the equivalent of quickly chugging 6 Red Bulls), causing disorientation, loss of balance, and best of all, pain.
You turn it on with a key in advance (so maybe wait until after you've got off the tube or refrain during torrential rains) and while activated you can actually see the arcing current in the strip near the neck. A rubber inset prevents self-electrocution.
While it's nice to feel safe, I'm not sure this would be necessary to wear on a regular basis unless I lived in a place particularly dense with pervs and muggers.
Just one question - is it still effective if the guy is on PCP?
See the demonstration (narrated in German, I believe, but you can easily follow) of a guy getting it good and the girl really enjoying it: