This has a long old history, which I won't get into but the recent thing is for both of them to comment on a pic that I had put on FB showing a hat I had knit. with the caption 'What do you think? Did I use the wool well?'
It was in order that I could show the friend who had given me the wool, what I had made with it and because I have not done any knitting for a bit and was rather proud of it.
I smiled slightly in the pic cos I was a bit embarassed to put up a show offy type of thing. Not a great big grin of check me, I am a big show off.
Sis only comment was 'Smile ever?' 
This is rich coming from the girl who was po faced for an entire day, in between reprimanding my children before I had a chance to open my mouth.
Mum came round, a big thing, she never comes to my house 'but your house is Tiny! ' and one of the first things she says is 'Where is this hat that you had no smile for?'
They just make me feel so sad that they have to be so negative before they might be in any way positive and that their first instinct is to say something rotten.
If I have ever said anything they just pull faces and say, we are only joking with you don't be so sensitive.
But it is just every time. 
I feel sad for me but for them too that, sis in particular, always sees the bad before the good and believes that it is ok to just go ahead and say it no matter how it might make another feel.