I'll admit he acts non-smegheadily very rarely, but he does do it. And the only other time _prior_ to OOT that he acts in a self-sacrificing way is when he tries to save Lister from the Cat (admittedly the Cat isn't very threatening as life forms go) and Holoship when he sacrifices his dreams of being an officer and of having a body for Nirvana.

OOT doesn't come from the blue, although there is plenty of Rimmerish cravenness to make it emotionally satisfying.