O.K. so what exactly does the rationalization for this look like...?

K. so, i went to a very cute kids party this past week-end and there was this guy there, the dad, actually of the birthday kid, and there was this lady there, a friend of the birthday kid's mom (Note: dad and mom were/are no longer an "item") flirting up a storm with aforementioned dad. So, here's the thing. I know that Dad has already shown that he can father babies at a somewhat alarming rate. Case in point, the current child spinning around like a little princess in front of us. Second case in point being the 1 year old Dad fathered with yet another lady he met at aforementioned kid's LAST birthday party .. Now, I'm not overly familiar with any of the players in this little scene but as I am familiar with this history I'm assuming an actual close-type FRIEND of the Mom would be even MORE familiar with the love-em-and-presumably-leave-em (preggers, it would seem) type of "dating" this Dad is into so.... I'm watching Flirty lady be all FLIRTY and I'm thinking, What in the name of dear sweet Jesus must she be thinking?? Seriously, did the frozen sperm get to be a little too expensive? Does she (seriously) think she's any "different"? And why (again dear sweet lord) at the kid's birthday party? Could she at least wait until the next major holiday so as to seem a tiny bit more original when she "mysteriously" finds herself with child/without boyfriend. K. sorry. I realize it's technically none of my business. Plus I'm probably being mean. Still. Why are girls so flipping weird?