One part vodka + three pineapple juice + ice into a cocktail shaker whatsit and shake it up. Pour into a glass (of any description...pretty glasses make it look pretty though) and then slowly pour on the creme de menthe (as much as you want tbh...1.5 parts is a vague gu-estimation).

Watch the green of the creme de menthe diffuse throughout the glass slowly and enjoy.

(Ice doesn't have to be shaken, if it isn't sometimes the Creme de menthe will accumulate in the ice cubes if they are hollow and that's quite nice sometimes)