Anything that harms Blossom. Whatever he won't say about himself. He really really hates her.

Though, if you can keep a secret, Blossom once said something like "You all work for that snake who seems to hate me for some reason," so it looks like Blossom doesn't even know what's going on.

...Hm. I'd hate to think Blossom would know something if you mentioned the Snake having a father. But... hm.

--You won't see me trying it.