Assuming you could keep anyone near it long enough to get a lethal dose. People are disgusted by it at the part-per-million level. These ammonium polysulfide ampules have been sold in joke shops for decades. They are used for clearing out study halls, and for delicatley placing under toilet seats, etc.
You do not have a Columbine Kid..you have someone who was a kid like I was! You could do worse, though it would be nice to find out what his intended target was...if it was beyond the practical joke stage, that would not be too funny.
A concentration of 1000 PPM (0.1% in air) causes immediate paralysis of the respiratory tract and death if the victim is not removed from the H2S environs and revived. Lower concentrations have adverse effects with continued exposure. Threshold alarm limits are commonly set at 10-15 PPM on alert detectors, with high level alarms set at 25 to 40 PPM.
Diabolically, one of the symptoms of H2S poisoning is the loss of the ability to smell, (even the H2S), which is why those of us who may be exposed are trained to test for the gas after alarm threshhold levels have been reached. Gas monitors are used in locations where contamination is possible.
Most inhalation victims result from entering an enclosed, contaminated area such as a tank, although releases in refining and production facilities and on drilling floors and workover rigs have claimed some lives also.
H2S safety training is pretty much standard in much of the oil industry as well as around gas processing and refining facilities.
People are killed by H2S in the oil field all the time, just two months ago two men died while servicing a tank battery. I just did a well where the rig hands had to work with air packs and air lines, it took three days to control the gas.