According to ChatGPT it's the skill of taking exactly one sip such that when you put the Guiness glass down the new beer level ends up precisely through the horizontal middle of the "G".

According to LadBible the actual trick was drinking a pint of Guinness while standing on his head.

https://www.ladbible.com/entertainment/netflix/netflix-execu...

I appreciate you taking the time to look it up so the rest of us don’t have to.

[dead]