You walk into someone's house, and you notice ____, a dead giveaway they're a dama nerd! I'll start: all of the dish towels are kendama related
When there's more wood hanging from their bedroom walls than used to construct the walls themselves !!
Well it's a bit lowkey but playing different woods made them wood connoisseur. they be like "look at that grain though" XD
If I leave my desk I have a dama in my hand. It doesn't matter if it's 20 steps to the door, I am grinding something. My house emanates a constant -clack-
Ooh here's another one: When everyone in your school starts calling you "Kendama guy/ kendama master/ kendama king/ etc."
When you have four of them on a Kengarden display.. and then a medium sized box full of them in the shelf by your bed.. as well as the top shelf of your desk..
...when you go to IKEA, or any furniture shop and you just know which furniture to avoid, thanks to your "extensive" knowledge of woods. Also, when you go to IKEA, take a good long whiff of the air, and go "ahh, nothing like Swedish birch".