Requirements: Playing on a real board.
A spillable beverage that would be annoying to clean.
Effect: Opponent avoids a certain area on the board.
Note: Close to no field research whether this actually works.
The idea is that you place your coffee or whatever right next to the Go board, so that it threatens to spill when a stone is slammed too closely to it.
This is based on what I found in the manga One Outs (Kaitani 1998-2006: chapter 24).
Read from right to left.
So this slightly unethical trick involves the player’s subconsciousness. That said, I have no idea if this actually works in Go and whether there are further conditions to fulfill.
I asked a friend once (long time ago) to try putting his ramen next to the board, in a friendly game against a 5 dan player. Allegedly, the latter subsequently neglected the corner in question for the greater part of the game (save for his very first move there in fuseki).
So it kind of worked against a player who is not overwhelmingly strong, but doesn’t suck completely either.
It may have to do with stone slamming habits, who knows?