I have handled situations similar to that. I took them aside and pointed out which behaviors were inappropriate and that they risked accusations of sexism if th

I have handled situations similar to that. I took them aside and pointed out which behaviors were inappropriate and that they risked accusations of sexism if they continued. I didn't have to in my situation but if it were necessary (e.g. they didn't alter their behavior and management wouldn't step in) I wouldn't hesitate to do a little public shaming. For example at assignment time or when you see him insisting on pair programming calling it out right in front of everyone: "You only seem to insist on pair programming with our female colleagues. That behavior appears sexist and reflects badly on the rest of us and you need to stop."