Find out what brand of feminine hygiene products your roommates use and where they keep them. Buy some, open the box and put them in a ziplock bag with an open jar of Icy Hot for a week. You don't need to open each individual wrapper, the fumes from the Icy Hot will permeate through and soak into the absorbent materials in the products.
Sneak some of the tainted products into your roommates supply and wait for the burning hell to begin.
My wife can, unfortunately, confirm that this works. My son didn't screw the lid all the way back on jar of Icy Hot before he tossed it into a bathroom drawer where she kept a box of pads. The fumes soaked into the pads and my wife had a quite a surprise when she use one. She was pissed as hell.