A Mentos-y Surprise!
Is your roommate a hardcore soda drinker? If they are, try and convince them to switch over the good side and drink good old H20 instead. If they insist on drinking the vile drink that discolors their teeth and internal organs, you will have to teach them an important lesson.
No, don’t spike their soda with hand sanitizer, if that’s what you were thinking. Instead, before filling an ice cube tray with water, make sure to pop a tiny Mentos into each ice compartment. When the ice melts, the Mentos will make contact with their evil carbonated drink, and they’ll immediately become a Hydro Homie afterward.