We're both parents of young boys, and she has a newborn girl as well. We were trading "war stories" of our sons and commenting on the whole "boys will be boys" mentality. I tip toed around the issue, not wanting to start a heavy discussion revolving around how that phrase sounds awfully pigeon-holing and trite.
Without unpacking that phrase, we both understood what it meant and the larger ramifications of it. In our society little boys will run around, shooting guns made of sticks while adults look on and shake their heads and mutter that well worn phrase.