Meh. 120v is nothing compared to our 240v when it comes to killing power. ;D
I've had a number of nasty zaps.With Trialex's idea you could even use two halves of a rectifier and you'd be able to detect the phase.
True, true.. 120V is for girliemen! Are you a girliemaaan? 240V for real men! 
Still haven't managed to get zapped by 240V mains, but I did get a good bang off of the flyback transformer in an old CRT-monitor rated at 30-40.000V. Of course, the current in something like that is dissapearingly small, but my vision still vent black for a fraciton of a second there. Scary stuff. ^^