I instantly remembered when he said that.
While we were all at the local park doing legal things that teenagers would do back in the late 2000s, my friend here found a rock at our old smoke spot that was unusually smooth and flat. He liked it so much that he took it to the woodwork classrooms at school, drilled a hole in it, and hung it on a necklace.
When we asked why he weanwearing this dinky-ass pebble on his neck, he claimed it prevented him from ever getting food-related illnesses: wouldn't get food poisoning, couldn't over-eat, was able to ingest anything (prior to him finding The Amulet, a few of us used to play a game called "Devil's Piss" where we would take turns shoving random food bits into a bottle of coke, and the first person to take a sip would get two dollars from the other players).
When we all asked him for the proof that this rock is magical—because nobody believed him, obviously—he said to meet him behind the History block at lunch, where he said he would drink two litres (or half a gallon) of milk in one go and not puke.
We met him there, and about ten of us all watched him down a whole bottle of strawberry milk in two or three breaths.
He jumped up and down and punched his stomach to prove it.