Easy, tell your GM exactly why you want the feat and what you plan to do with it.
If you're not willing to do this, then he was right to deny you access.
If you tell him and he disagrees, try to take his decision with good grace. After all, you trust him enough to be your GM. You should have enough confidence in him, to believe he has a reason for saying no.
Besides, if you want revenge on your GM sleep with his sister or slip laxatives into his jolt cola. OOG revenge is so much easier than IG. (Disclaimer: On advice of legal representation I wish to point out that this paragraph was in jest).
Seriously though, he's the GM. You can't win. Ever.
Why?
The Tarrasque can be templated.
