Admittedly undercooked idea, but how about showing the intuition for class complexities as filling containers with different shapes:

O(n) is a mug 🍺 (it fills up linearly)
O(sqrt n) is a cocktail 🍸
O(1) is a plate 🍽️ (it is immediately full)

nvm cocktail would be O(n^1/3)

stupid humans and their 3 dimensions