Gonster is a cocktail based on the energy drink Monster Energy Nitro and the beer Guinness.

The name is a portmanteau of the two ingredients, the "G" coming from Guinness and "-onster" from the energy drink. The drink is also referred to as a Billie Irish.^[1]

The drink is made by pouring half a can of the energy drink in an empty pint glass, followed by slowly pouring the Guinness over with the help of a spoon. This prevents the two drinks from mixing, and the green Monster will occupy the lower half of the glass, with the dark beer remaining on top.

Gonster has been circulating around social media since 2020, but it was during the spring of 2024 when it reached virality as an internet meme following St. Patrick's day, when media of the drink were shared millions of times in a matter of days.^[1]