I think when ZZ top expressed this sentiment, it may have been a little different than the one that I scream to myself inside of my head.
My oldest is Mackenzie (Kenzie for short). She is a beautiful, brilliant and verbal child with precocious tendencies. When she was a baby she slept for 12 hour stretches at night, didn't cry much and preferred not to be carried around. When she was a toddler, she never threw tantrums and would calm from a fit of crying when I simply said, "Can you calm down?". People used to credit me with her good behavior and I had a sneaky suspicion that I had nothing to do with it...that it was just the way she was.
I used to watch my good friend with her boys, who were a little more high maintenance at the time and think, "That looks hard, Kenzie doesn't do any of that..." Turns out I was a Smug Mother of a Girl.....
Smug mothers of girls can be identified by the slightly confused look of sympathy given to mothers of toddler boys, like "Why are they doing that?, don't they know just to ask them to calm down and they'll stop biting/whining/screaming/jumping off the bedroom dressers...." My poor friend Dawn bore this unconscious attitude from me with grace, only saying "I can't wait until you experience parenting boys..." as her only indication that she knew what I was in for, and that it would be a whole different ball game. Then BLAMMO, my twin boys were born and they haven't slept through the night or stopped screaming yet and they're three!
So now Kenzie is 6. I heard when she was younger and I only had the one that girls were easier when they were babies but harder when they were older. "Surely not.. I thought, Kenzie is a reasonalble human being and will continue to be so."
Then reality bitch-slapped me at age 4. There was a new sheriff in town, and her name was ATTITUDE, she was flanked closely by her twin deputies, Passive Aggression and Demandingness. Now when I wake her up in the morning, the first words out of her mouth are "Am I getting my allowance today..I really need Skwinkies, I'm the ONLY one at school who doesn't have them." and MOM, this and MOM that, peppered liberally with eye rolls and sighs.
So now the boys are at their worst/hardest age and the girl is as her worst/hardest age.
The smugness has gotten SO smacked off my face, thanks for the foreshadowing Dawn!