'I ain't your friend!!'

How to break friendship with Am Fah/Jade Brotherhood?
I really need to break up with Am Fah so I can get Quivering Blade skill from that Am Fah boss.

I have sonewhy drunk from the cauldron of corruption or whatever it is, and now I could do the 'Masters of Corruption' quest. I'm really pissed if I have lost the chance of getting 'Canthan skillhunter' rank

Just complete the quest. If you've drunk from that cup then you have a negative degen on you all the time, so you really need to complete and stop the degen.

No I know how to get rid of degen, I have currently cancelled the quest. I just need to know is there a way to make Am Fah my enemies again.

Sun, the Quivering does not appear until you've completed "Drink from the Chalice of Corruption" or its alternative, "Refuse to Drink." Finish either one and you'll be able to find him.

As I understand it, completing 'Masters of Corruption' will make the Am Fah hostile once more:

quote from the Guildwiki article:
"Brother Tosai will beg for his life, bargaining for mercy with the removal of the chalice's degen effect. Once removed, the quest is complete. From then, all Am Fah will revert to being hostile."

Oh?
That solves it all, I'm on my way to completing that quest.

Thanks

you should checked wiki first anyways.

For future reference:

You can cap the skill before making the Am Fah your friend.

You can unlock the skill on another character or through Blathazar Faction and then use an Elite Warrior Tome.

I did the latter on my title hunting character as I prefer having the Am Fah as my friend. Makes running around in those areas much less of a hassle.

and even if they hated you for life you could use a tome to obtain your title

I am not native english-speaker, so hate to admit I didn't first know what 'revert' means I thought it means they stop being enemi.

Ah, quite alright. For future reference, "revert" (verb) means - to return to how things where before

example, the arm fan started out as hostile, became friendly, and then "reverted" to how they were before, by becoming hostile again