Go read her's first.
What he should have done ...
I acknowledge receipt of your letter dated the 9th this month. I was well aware of the approach of Buffy’s 18th birthday. I have been making plans to celebrate for several weeks. I wish you to note the following:
I have no intention of allowing my Slayer to undergo the barbaric custom you refer to.
I will be informing Buffy of this fact once this letter has been posted.
If you, or any member of the order appear in Sunnydale in order to conduct this test, you will find yourself forcibly evicted.
Yours, Rupert Giles.
ps. I quit.
Resignation: Part 2
To: Quentin Travers and all the members of the so-called Watchers Council
You big bunch of pompous, self-righteous, jerks. How dare you spoil my birthday party.
Quentin, you prick, this part is just for you.
If you or any of your goons ever come to Sunnydale again, I will forget the rule that says the Slayer never kills humans. You had better be glad that the doctors just told us that Giles will be okay, or there is no place in this, or any other dimension, that you could hide from me and my friends.