Which part specifically of the GIEC memo was Damore being an asshole?

The whole thing was unnecessary and not part of his job AFAIK. It was also a giant, dressed up, thinly veiled "fuck you" to any of his female colleagues even if he didn't have proper social awareness to realize it. The scientific claims on gender differences were exaggerated and aloof, in part because even if you believe such a claim in terms of averages, making social determinations based on them ranges from flatly idiotic to against the law (for good reasons).

He should have stopped himself when he needed to add a disclaimer that he doesn't believe in prejudices and stereotypes. The need for such a statement is a giant red flag at which point one can ask themselves some critical questions.

When he is fired for this, a lot of conspiracy theories abound, up to and including in this thread. But he should work on the awareness to know what he was saying is a fireable offense by reasonable people. Apparently NLRB concluded the same.

This is all not the same as him being unforgivable or a bad person. In googling after this thread I noted an interview about him and autism. So he may very well deserve our sympathy and have an alternate explanation. The way people on forums like this one use him to allege a massive conspiracy at Google remains unwarranted despite this.