Idiom or quote that means "Decided to be the opposite of [a person]"
... I decided to be the anti-{person's name}.
Superman to the rescue again:
Having met John, I decided to be Bizarro John
Bizzaro is a DC comic character whose powers are the exact opposite of Superman's.
Also see: The Bizarro Jerry, a Seinfeld episode where they meet a polar opposite of Jerry.
The word has decent permeation in pop culture. If your audience is familiar with Superman and/or Seinfeld, you should have no trouble getting your meaning across.
[Wikipedia]
EDIT: Thanks to ScotM for the Urban Dictionary link