post a better weapon than the previous weapon.

Basically, just see what weapon the last person to post uses, then post a weapon stronger than that one. The only rule is that you make it gradual and don't say something like "Nuke!" right away.
I'll start with something small...

Pencil

pen

ruler

steeltoe boot

Baseball bat

hammer

cigarettes

crystal meth

cancer

syphilis

Smallpox

Vaccines

touche!

AIDS

ebola

Human hands