How come a sagittarius can be so vindictive?

I'm a sagittarius and when someone makes me angry I pay it a 1000 times back. Sometimes my friends and especially my sis call me "devils daughter". They said to me that if I want someone to suffer than I'll make it in the most horrible way. They say that when I tell them my plans (I like to think of more than 1 way to crash my enemy) I'll choose the most horrible and they say the others are horrible too but the one that i choose will let my enemy cry like a baby and they will become scared to death with me. I think that all my plans are the same there isn't a most horrible and I don't think that its so bad (even if I made some people cry). Maybe its the influence that I have gemini moon and scorpio rising (I heard that they are the most vindictive signs of all zodiac signs) But i don't think I'm such a bad person not to the point that others call me devil