What should i do!?!?!?

i am sick and tired of this guy!!! i HATE him. When i was in 8th grade short, a wussy and chubby this guy used to pick on me now that im 15 tall, slim and fearless i feel that i should exact my revenge on him! Just recently i found out he had with my bestfriend and left her so now i want to stab him!! should i kick his azz or stab and kill him??? he swares hes a gangsta when he is really soft and pathetic!