Consider x a distance between a place where an event took place at time t1 and a brain. At time t2, if x is larger than c * (t2 - t1), it for sure does not affect the brain.

Sure. Except then you need to define c. Back to square one.

c is commonly used to represent the speed of light[1]. The commenter was saying that an action sufficiently far away cannot affect you immediately, because the information of that action's occurrence cannot move faster than light. I believe this is generally regarded as true by physicists, although there are some ideas for circumventing this limitation.

I think they were making a joke.

[1] http://en.wikipedia.org/wiki/Speed_of_light

Thanks. :-)

(I thought "speed of light" at first, but didn't think of a way it could be applicable.)

c is speed of light?