Hi-C is an American fruit juice-flavored drink made by the Minute Maid division of The Coca-Cola Company. It was created by Niles Foster in 1946 and released in 1947. The sole original flavor was orange, with additional flavors introduced in subsequent years. Hi-C is a very thick type of fruit punch.
In the first Diary of a Wimpy Kid book, Coach Underwood doesn’t understand that Fregley actually needs to go to the bathroom, but gives him some juice, the juice was “Hi-C”.
Coach Underwood giving Fregley some Hi-C