Well, that's pretty much escalating it to a point where all discussion becomes useless. I say that is pretty weak.
I'm going to do two things here:
1. I am going to respond to the ontopic part of your attack.
2. I am going to go offtopic, see your weak nihilism and raise you strong nihilism.
Rational means: 'making the optimal decision to further your goals.' The only thing I needed to prove was that there could be reasoning behind not wanting to be seen as weak. I went a little further and stated that there often is reasoning behind not wanting to be seen as weak. I repeat: rational conclusions are not universal; they depend on your goals. What is rational for one, may not be rational for another.
I agree, there is no goal in the universe. I'd state it even stronger: there can ultimately be no ultimate goal of the universe (this particular universe may have an ultimate goal if it is nested in another universe, but that is sort of cheating with the word universe). The word goal is dependent on time and on a ranking of configurations of the universe. Coming closer to your goal means that the configuration of universe has changed in such a way that it is more likely that the set of configurations that define your goal will occur. Attaining your goal means being in the set of configurations that define that goal.
If all configurations exist 'simultaneously' (i.e., time is just another dimension), then the whole notion of 'moving to another configuration' is nonsensical. There can be no goal if there is no passing time.
Even if the universe is really only in one state at a time, there is no absolute reason to value one configuration over another. Reasons can emerge within the universe, but not outside of it. I.e.: all species have a basis to rank certain configurations above others (the dinosaurs might have certain preferences concerning asteroids), but without this emergent value system, there needs to be an inherent value system that defines which configurations of the universe are more desirable than others. The universe doesn't work that way: it has no concept of values. It is as you said: it just exists; it just happens. There are configurations that are statistically more likely and in that sense one could argue that the universe 'favors' those, but that is a far cry from our intuition of a 'goal' (heat death doesn't seem that interesting).
Finally: if there happened to be an ultimate goal, what would we do after attaining it? Suppose the ultimate goal of the universe is pushing a big red button in some crevice on Mars and we manage to push it. Then what?
In more technical terms: the set of configurations that would define an ultimate goal is necessarily relatively small and ranked above all other configurations. The only option when reaching it would be to 'roam' indefinitely in that limited set of configurations (although admittedly, it can still be an infinite set).