I purposefully avoided laxitives, for several reasons:
1) it's illegal, and my dad was a cop, and I knew better. Adulteration of food stuffs is a felony. Habenero juice, however, is not a drug, and therefor adding it is not food adulteration, and is perfectly legal.
2) the mark in question had no problems wolfing down 2/3 of a very large sheet cake by himself. He managed to inhale 5 brownies in under 3 seconds, so I feel my observation about the liklihood that he would OD being too great were justified.
3) like a cat, bad behavior in children needs immediate consequences. Laxitives take too long to act. !!BROWNIE!! Had just enough delay for the crime, before springing the punishment.
It took me 2 weeks to work out how I would perform my vengence, and do so "totally legitimately". Habeneros are not something my family usually buys, and I had to arrange their purchase. This means I needed a cover story, and a bunch of other things. Try explaining why you, as a 12 year old, need a bottle of everclear for instance. (I said I wanted to try making a flaming plum pudding.)
I worked out that capsacin dissolves in oil and alcohol, and not water. (This is why milk works to soothe it, but water doesn't.) By using alcohol as the solvent, as the brownies baked, the capsacin would dissolve in the oils in the chocolate of the brownies as the alcohol baked off. This is the reason for the time delay. The problem I had was that this was pre-internet, and "evil brownie of doom!" Is not something you find in a cookbook. Figuring out how many crushed seeds you need for maximal effect was not easy. (You need about 4 tablespoons of crushed, dry seeds per cup of solvent for maximal burn.)
Imagine a 12 year old keeping all this a secret for 2 weeks, working it all out, before springing the trap. That is what made my mom unhappy. I had to lie consistently, and to solve a wrong with another wrong. That was why I got grounded. But nothing feels so good as a scheme falling into place.