Guest blogger Liz Fenton: I've recently picked up a mommy nemesis on the playground. (But for the record, I really do like to play nice with the other mommies!) Don't judge: I'm betting that you have one, too. Maybe she's that mom who always looks down and ignores your cheery hello at pickup each day. Or maybe she's the one who can never seem to remember meeting you, even though you've been introduced several times. Or possibly she gave you the evil eye when you were rocking your sassy new boots on back-to-school night. No matter the circumstances, she has now become your mommy mortal enemy ....