I don't expect everyone to understand all about adoption. I didn't, before I became an adopter. I hate it when people react with prissy, precious shock if someone doesn't know the 'correct' way to talk about minority experiences.
What does get my goat is people who don't know and don't care to learn. Who are more interested in spouting their own uninformed opinions than in listening to the reality. The thing that most bugs me is when I'm trying to talk with a friend about the realities of parenting my adopted dc is when they instantly assure me 'But all children do that'. So many otherwise lovely people do this! I'm sure they don't mean to do so, but it kind of implies, "I'm a real parent so let me tell you what this is about". Particularly irritating as I am also a birth mother, so I do have a good sense of the similarities and the differences.
And I also get wound up by threads where the OP is wondering whether they should report a situation to social services, and posters keep popping up to shriek, "My child sleeps on a mattress! My child gets grubby! My child is naturally thin! OMG if a social worker came round before I went to the supermarket they'd find empty cupboards! DOES THIS MEAN THEY'RE GOING TO TAKE MY CHILDREN AWAY?" I have to leave the thread because I get the red mist and want to post, "Stop making this about you and your non-problems, you fool - try to understand the level of what children have to endure before they are taken into care".
Oh, and the threads about drinking in pregnancy, where the political orthodoxy is that we're absolutely opposed to any kind of policing women's bodies and anybody who talks about what is happening to the child in the womb is a misogynist fascist. I am, incidentally, completely pro-choice (worked in abortion clinics for many years) and am opposed to the kind of policing of pregnant women's behaviour that we see in the US. But I am also the mother of a child who was exposed to drugs and alcohol in utero, and the realities of that have to be understood by all those who join in that debate. In trying to explain this, I have been told I'm a disgrace, that I should be ashamed of myself etc etc.
But most of all, it's just very irritating when women struggling with infertility are told to 'just adopt'. Adoption has been a wonderful thing for me, but I would never proselytise for it, and certainly not to a woman who desperately wants to grow a child in her own body.