I had a similar. When my older brother was headed back to UT one thanksgiving, my dad went ot check my brothers car for air in the tires, fluids, etc. Came back in with a bottle of vodka under each arm (that cheap crap in the plastic bottle, McCormicks or something?) Brother was pissed. Dad was grinning. I was scheming.
A few months later parents were gone and I had a big party. Took a screw driver, popped those caps off without breaking the safety seal and poured the vodka into milk jugs. Filled the bottles with water and put them back. My parents drank a reasonable amount, but it was alwasy scotch or bourbon, so in the next 4-5 years, they didn't finish the bottle of decent vodka they had much less get into my brother's stash.
Day finally comes and my dad is getting ready to make something with vodka for everyone at Christmas. I ask him if I can see the bottle, he hands it to me, and I proceed to chug down like that scene in Animal House. My parents just stare at me in horror. I didn't drink the whole thing, but I slammed it back down and said "Thanks, I really needed that!"
Then my brother starts laughing, I start laughing and my parents are realize something is up. Brother had taught me that trick about popping tops without breaking the seal. He says "You son of a bitch, you drank my vodka years ago, didn't you?" I say "yes, and it was a hell of a party!" Then we explained what I'd done. Mom thought it was hilarious. Dad was impressed but then made me get in the car and go buy him two new bottles!