Since I last adjusted the pads, the front brake on the Red Baron has developed a squeal. Interestingly, this vibration propagates back up the cable to the lever, which can then be heard squealing in sympathy (maybe this is normal, and it's just the Baron's geometry putting the brake levers close enough to my ears that I've noticed it). Anyway, I can imagine the same effect at a lower frequency feeling a lot like a mild electric shock.
That said, being zapped by a dynamo hub feels an awful lot like an electric shock too (DAHIKT), but I'm struggling to imagine how a current path through the brake lever would happen.