* A strong focus on being "right" over working collaboratively (especially in domains with no right answers).
* Hyper competitiveness - to the detriment of effectiveness.
* A lack of empathy (e.g. PRs with "your code sucks, suck it up and stop being such a baby").
These things are hardly good from the perspective of any software developer (except particular kinds of men who thrive under these conditions) but they're particularly off putting to women.
I tend to find that this aggressive behavior is most frequently exhibited by "senior" developers who aren't actually very good or clever but have built up a reputation that they wish to protect. Some developers are very territorial.