This one turned out either better or worse than expected, depending upon whose perspective.
So, you know that one guy in your group of college buddies – always worried about upsetting the resident assistants, always has to leave the party or quit Mario Kart early because he's gotta finish a problem set in the morning – your basic anti-Aldo, we'll call him Odla.
Every night, before he went to bed, Odla would fill up his clear one-liter water bottle, and every morning, he'd chug it before getting out of bed – Odla was into hydration (shockingly enough). Odla was also rooming with those kids who had the beer fridge and the N64 – so, it was only a matter of time before, two or three pulls of plastic bottle vodka chased with High Life (forgive me, I knew not what I did) after Odla went to bed, we decided to mess with that water bottle.
It was a clear water bottle, so we decided something visually arresting floating in it would be the best bet. We were drunk and broke, so sculpting something out of the play-doh somebody had left in the dorm lounge seemed like the best idea since sliced pizza. Now, our sober selves would've immediately realized that something made of flour, salt, food coloring, and dihydrogen monoxide, left in a quarter gallon of water for several hours, would probably dissolve – but, we hadn't seen our sober selves in a while, so, we slapped together an artistically-interpreted "gin fish" whose hung-over visage would greet Odla in the morning, and in an operation owing more to the sleep-deprived coma in which most college students repose than to any particular stealth or daring on our part, we set the gin fish free in Odla's water bottle before retiring to our own sleep-deprivation (and cheap booze) induced comas.
I am generally a bit of a misanthrope who enjoys his privacy, but in having chosen to live alone that year, I regretfully did not get to witness first-hand the look on Odla's face when, upon sucking down about a third of that liter bottle, he realized that, rather than the water he was expecting, it was full of cloudy, floury, particolored brine into which our star-crossed gin fish had dissolved.