It might just be me, but I find it really irritating when people who have children when you don't, or have older children than you, talk to you as if they are the authority on being a parent, and know better than you, just because they did it first. It also has a tone of 'im better than you coz i have kids/ had kids before you did'.
My favorite example is when someone says 'you don't know what tired is until you have a child'. Really boils my piss. There are a plethora of reasons why someone might be tired in their life, not just because your baby wakes in the night or is high needs. Its this sort of attitude, that implies that all life experiences except child rearing are invalid, that i find so desperately infuriating.
Anyone else???