They do give a shock
"My younger brother helpfully introduced me to the delights of opening up a disposable camera many years ago by shocking me in the exact same way, and unlike a police taser device, I did not collapse to ground, convulse, risk a heart failure and piss my pants."
Try charging the flash first ;o)
Disposable cameras have a capacitor to power the flash and believe me, it outputs one hell of a poke. I'd be surprised if you didn't fall over after getting shocked by this.
"Someone" i know was given a disposable camera without the front panel on when "they" were younger by a "friend" and "they" got a bit of a buzz from the terminals. So "they" charged up the flash and put it on "their" mates arm and he dropped to the floor!