The Buddha Has No Bounty on His Head

"The Buddha has left the road and renounced the next road/s as well. The Buddha seeks only surcease from all pain and desire."

However, if you are properly Buddhist, then the desire you release is the desire not to desire. Let go of the desperate quest to put a stop to desperation. I don't have a snappy line for pain. I think of it this way: either you deserve the pain or you don't. Definitely one of those. If you deserve the pain, then accept your own responsibility. If you don't, then take comfort in the fact that your suffering is unjust. If your immediate response to the pain was working, we wouldn't be having this conversation, and it's time to stop. 

But, yes. A proper Buddhist is a not-Buddhist. Buddhism proper is a soft suicide cult, for devils who accept they shouldn't exist but are too squeamish to take a knife to themselves. (The non-squeamish set has already ceased to exist.) An ideology of ego-death is always going to cash out to an ideology of ideology-death, thus killing itself, exactly as originally intended.

If you're in desperation and pain, then you are in desperation and pain. Pretending you're not is nothing more than a childish lie. If you wish for these things to go away, then it is true that you wish for these things to go away. Pretending you don't is nothing more than a childish lie.
Sometimes, you can make them go away. Sometimes, you can't. Sometimes trying to make them go away only makes it worse. It depends on the situation. Trying some solution which doesn't depend on the situation is to say you can control the world in a way that doesn't depend on the world. You may guess what I have to say about this: it's a childish lie.
Sometimes you can override a desire directly, it is true, but this is only when a deeper value overrides a shallower value. Pain, ultimately, is the name we give to the quale that indicates/instantiates failure. The only way to give up failure is to give up existing; to give up having any values is to not exist. To perceive at all is to make distinctions. To see [that is] is also to not-see that which [that is] is not.

Are there bad koans? Sturgeon's law applies perhaps especially to them. Should you kill the Buddha if you meet him? Depends what you mean. Imagine meeting the Buddha on a road. What is that like? What is the situation? 

Some imagine immediately trying to abase themselves before the Buddha. Or demanding something. Perhaps the Buddha demands something of you. Maybe he tries to follow you? I don't imagine any of these things myself, though. Perhaps we can shortly say it this way: if the Buddha tries to direct you off your own path, kill him. It doesn't matter how much [better] his path is than yours, because you can't use it. It's not your path. Your path also needs to be the path which is yours.

Casual googling shows that the Buddha you're supposed to kill is a fake Buddha. They're saying you won't meet Buddha on the path. However, even the Buddha makes mistakes. Even in the spiciest scenario, where you meet the real Siddhartha on the road, if he screws up, then killing him may well be the right thing to do.

It's hardly guaranteed, though. This is what makes this a bad koan. If you meet a koan on the road telling you to kill the Buddha, kill it. Kill it, cook it, and eat the meat. The Buddha telling you to kill the Buddha is a fake Buddha, just like his koan said such a Buddha would be.

It is very likely that any Buddha you meet would be a fake one. If you can see it, if you could plausibly kill it, then it's not the Buddha. Even if it's really from the Buddha, it's merely a mask being projected, from one side or the other. Not the thing itself.

I like to think Siddhartha is no more Buddhist than Yeshua was Christian. The alternative is too depressing.