I got alot of undercurrent in that Christmas scene. I always thought that Remus and Sirius had it out about Snape's loyalties and Sirius had gone to Dumbledore with his suspicions and been summarily dismissed.

Some people have said so....

And then he talks about understandably inheriting hate.

The whole scenario smacks of backstory. Remus was continuing a stance that had already recieved disdain, not being spineless for sure.