> We probably understand this word very differently, because as far as I'm concerned, rationality (rational behavior) is essentially an exercise in behaving optimally, one that is thus strictly relative to some particular context.
No, that's completely consistent with my understanding.
Adopting identity labels doesn't follow from that, however.
The parent comment has been talking about exactly people who have been turning this into an identity: https://en.wikipedia.org/wiki/Rationalist_community
If this doesn't apply to you, great, but then we're talking past each other.