I'm borderline T/F and E/I. I was more introverted and disconnected when I was younger (I'm 27 now). I used to do this all the time. It's a fantasy. I used to imagine punching teachers out and the fallout (crowds, expulsion, etc.). I sometimes still flirting with the fantasy of crashing my car and dying. I would never do it. Really, never. Even if I was depressed (and I kinda happen to like depression, anyway). But I fantasize about it. It's taboo. Taboos are always fantasized about. In an INTP who's mental life is dominated with possibilities and boundaries, it makes a lot of sense.
Looking back, it's possible that I was angry at someone or myself. That's just the way it leaks out when it filters through the INTP brain. I'm not a therapist, but I would say: it's not a problem, but if you have underlying depression, anger, and sadness, it's worth investigating those things and resolving or making peace with them.