Here's an idea.

For those of you out there who are still working in the Chem lab for whatever reasons, here's a really fun thing to do:

1. Find a colourless alkali (eg. Potassium Hydroxide, KOH).
   
2. Pour it on someone's shirt, pretending it was an accident and pretending it's only water.
   
3. Steal some pH indicator.
   
4. Drop a drop of the mentioned substance in Step 3 on the subject's shirt.
   
5. Enjoy the subsequent observations.

Note:-

An alternative method towards a more unliked subject, as Shu Min suggests, would be to replace the colourless alkali in Step 1 with an alkane (which is obviously colourless) and replacing Step 3 with "approaching the target with necessary precautions and striking a match and throwing it at the said target". Step 4 would then be irrelevant. Hence, skipping it and going directly to Step 5 would be the advised measure.

PS. BW'S PLAY DURING DRAMAFEST(E) 2009 WAS AWESOME! THE SCRIPT WAS THE BEST!!