Several people in the comments got the point of my endogenous sexism scenario.  Namely: Friends pass a stricter selection filter than spouses of friends.  If you think poorly of someone, you won’t be their friend.  But if you think poorly of the spouse of your friend, you’ll probably put up with your friend’s spouse to preserve your relationship with your friend.  As long as people tend to make more same-sex friends, then, men’s male associates will seem better than their female associates, and female’s female associates will seem better than their male associates. 

Two lessons:

1. When a man doesn’t like his wife’s friends, or a women doesn’t like her husband’s friends, it’s not surprising.

2. By itself, #1 does not imply sexism.  But #1 combined with statistical naivete readily leads to sexism.

How strong should we expect this effect to be in the real world?  Hard to say, but friendship is strongly segregated by gender.  The General Social Survey, for example, asks about the gender of your best friend.  Same-sex besties outnumber opposite-sex besties by 4:1 for men and 6:1 for women.


P.S. Don’t these results imply quite a bit of unrequited best friendship?  Hmm.