Split

Splitting the G/Split the G

A daft craze that “refers to taking a substantial enough first gulp from a pint of Guinness that the level of the remaining beer in the glass is directly through the middle of the "G" in the word Guinness, which is printed on the glass.”

Bejesus!

https://www.urbandictionary.com/define.php?term=Split%20the%20G