When one takes a definitive action that in turn, becomes detrimental or overall unfavorable for them. Basically, to do something stupid that only affects you.
Also (in certain cases), see douchebaggery or Back Door Braggart .
1.) "Dude, did you hear that John broke up with Ashley?" "Yeah man, and I saw his new girlfriend... that was a huge self-fuck on his part..."
2.) "AGH, I stayed up until 4am doing this paper for English, and I left it in my printer! I cannot believe I just self-fucked my grade."
3.) "Yeah, I heard that Neil was just nerdjacking the whole time on his date. Total self-fuckery."