This is kinda long, but recently my brother was stressing about when their baby was conceived because the date the doctor gave them was 'wrong'. (you know the number of weeks since AF not the number of weeks since Actual conception - or 'the deed').
I went forth in great details as to the logistics of it all - relating it to my embryos and the EPU and the ET etc. Ooops. I confused the heck out of him and probably told him some things about his lil' sis that he didn't need to know
In the end I just said 'trust me, this is one thing i DO know'.

I forget that most people never have to know about all of nitty gritty dates and details - they just get the fun part