Had a Columbine phase in mid-highschool, which basically amounted to emulating the shooters as much as possible. Listened to KMFDM and Rammstein, kept a journal with edgy/angsty writings, and wore a trenchcoat to school (or at least the longest coat allowed at mine), all because the shooters did. I even got into Doom because of them, though the sheer number of wads kept it enjoyable even after that phase was over.
Whole thing stemmed from playing that one Columbine RPG, thinking "whoa dylan is literally me", and researching the shooters out of curiosity. Not surprisingly, it ended right around the time I started working up the confidence to talk to people and make friends.