Board Thread:General Discussion/@comment-4504826-20160426040035/@comment-27907368-20160427015822

One of the most obvious pieces of information is from sans himself. In his boss fight, he says that he hoped that he could befriend the anomaly. If coming back after being dunked, he'll say "i guess we never were friends. don't tell the other sanses that."

He recognizes that other hims are going to be ignorant of the protagonist being a psychopath.