When the first thing you do while waiting to leave for class is hop on here (like I'm doing right now, because it's better than waiting an hour on campus for things to become open).
Also, when you've managed to convert two (and somewhat convert one) people to Touhou.
Also (second 'also'), I just saw a sidebar... event... ad... thing... on facebook. It said something along the lines of "This September, Be Easy."
I read it as "This September, Take it Easy."
Also (the third one!), when you want to learn about new series partially due to finding about them in a Touhou video.
Like this one. (Around 1:05, wait for the style change.)
It's also because I recall seeing that style somewhere, and it's gonna bug me until I watch/read the series... But mainly because of Fukumoto'd Hatate.