While my seven year old boy fantasized about extremely unsanitary ways to remedy this obvious failing, I couldn't keep my own mind from spinning. I resisted the temptation to experiment till now, but the allure of this contest and Think Geek was just too great for me.
I present here, the smelly whoopee cushion!
Step 1: What You Will Need
Glass jar with lid
silicone glue (optional -- I didn't need it)
Small clamps (from office supply store)
1/3 cup ammonia
1/2 box of matches
Step 2: Preparation
Drill two holes in the lid of your jars so that the pieces of flexible tubing fit snuggly.
Seal the tubing to the lid with silicone if necessary to get an airtight fit.
Step 3: Stink Bomb
Let sit for one week.
The sulphur in the match heads reacts to the ammonia and produces ammonium sulfide, a chemical with the odor of rotten eggs.
Step 4: Prepare the Prank
DISCLAIMER: the match heads and ammonia are supposed to sit for a week... to make the contest deadline I only had time to to let it macerate for a couple days. At this point the resulting smell is still closer to ammonia than rotten eggs so the experiment is not fully successful -- yet. I'll report back with full results in a few days. If it doesn't work other concoctions can be used with the same basic set-up.
CAUTION: don't blow this air in any person or animals direction. It stings. Just thinking about what would happen if you sucked the air in rather than blow it out makes me hesitant to post this instructable.