After my daughter died there was this woman who kept on telling me she was going to hug her daughter a little bit tighter because I couldnt hug mine anymore, sometimes her daughter was with her and she would literally hug her in front of me, sharing her daughters achievements with me so i could have a little bit of what i lost etc. Just an acquaintance that i would bump into every now and then, but every single time she said something along these lines.
It was on my daughters birthday that I bumped into her this time, I was buying a cake (we do a cake every year for my son and daughter who died), her dd was born around the same time as mine so she would have known.
She said "oh how heartbreaking, having to buy a cake for your dd who cant appreciate it, count yourself lucky though, in a couple of weeks I have a house full of kids for my dds party, what I would give for some peace and quiet".
I think it was the years of pent up rage at her thoughtlessness that made me shout at her 
"I dont count myself lucky at all, but since you do how about we swap places and you have your fucking daughter die on you so you can enjoy the peace and quiet that brings"
She burst into tears in the middle of the supermarket, I pretty much stormed off calling her a stupid bitch for good measure.
As soon as I got outside I regretted it instantly, as thoughtless as she was I guess it came from a good place?
I still havent spoken to her again and I see her semi regularly. That was 3 or 4 years ago now.
I know I should apologise, but I wont because, to be honest, my life is that bit easier without these interactions with her. I do feel bad though.