Distilling Alcohol. I wasn't of age at the time, actually was still in high school, and had a hard time getting alcohol, so I decided to make it my self.
Designed and built a reflux still with embedded temp sensors, a condenser, and one-way air locked gasoline containers for fermentation. I used sugar and yeast to ferment giving me ~10% abv, then ran it through the still 5-6 times to get ~90% abv... it was rocket fuel. I also sent the final samples to a chem student I knew to test for methanol as a precaution. Finally filtered several times through activated carbon to get any final impurities out.
It was the best vodka I've ever had so far, no burn and extremely pure ethanol. I only made a handful of batches before the excitement of it ran out.