I recall this notion from Asian martial arts that there are two “soft spots” on the sides of your skull that, if someone were to press firmly in with their thumbs, or insert a needle or filament into, you would die almost immediately.
Is this true or just something fanciful? (Not a need answer fast…)
I don’t think so, at least with adults. See Coronal suture.
There are plenty of places on the head/neck that you can use to incapacitate a person. How about pressing firmly in with your thumbs to the eyeballs? Or the trachea?
This reminds me of the thread about the firm blow to the side of the neck. Searching finds several SDMB threads on this, but not the one I’m looking for…
This thread. I don’t believe this was demonstrated to be true either.
There is a region of the skull called the pterion–sort of between the upper ear and the eyebrow, where several skull bone sutures meet.
It is significant on two counts: First, the skull is not as strong there, and second, an artery (middle meningeal) is underneath. So if you get a blow there and a resulting bone fracture lacerates the artery, the high-pressure bleeding can be as lethal as the blunt trauma. Definitely not “instant,” though.
We pay special attention in the ED when a child has a skull injury over the temporal region, but I have no idea if some individuals are strong enough to break an adult skull there with “thumb pressure” alone.
“Needle” and “filament” are too vague for me to comment on. You could get through with a sturdy enough awl probably, but I think there would be better places to direct a sharp pointy thingy if you want to dispatch someone. The front part of the brain (your brain, anyway 
) is not very important. For sure no reasonably skinny pointy thing is going to cause “instant death” anywhere in the brain except maybe somewhere in the brainstem on a really (un)lucky path.
What about right behind the earlobes? That feels like a pretty exploitable crevice there.