I'm thinking of bringing a knife to school
You're joking, right? Why are you thinking about bringing a knife to school?
Nobody will mess with me if I brought one.
Bringing a knife to school can get you into a lot of trouble with the administration. Also, if you get into a fight and don't know how to use the knife properly, it can be turned against you and you could be seriously injured.
Nobody will bother me with the knife, and I will know how to use it.
You are going to get in a lot of trouble. Schools and the police don't take this kind of thing lightly.