for you, craftymcgluestick. That is absolutely how I felt for a few long years before things seemed to simmer down a bit. Gah. I had my feeling hurt several times because people were getting things for my dd that were special for *me* to do for her, and overstepping my experiences, or were 'being better' than the time-spent homemade things that were important for me to give and make for her.
Seriously, though. I think there were a string of incidents were I just hurt people's feelings. Word got back (through the kids usually) that we'd gotten rid of some xyz thing that grandma had bought as a gift, or fragile gift items got broken, or I let the kids *do whatever (dump in water, paint, etc)* to their toythings that were gifts. Once or twice I just stepped in, took item away (for example there was a wooden sword toy that was, truly adorable and well made - but two 3 y/olds were being encouraged to hit at each other with, and dh had actually talked with grandma about how it wasn't exactly a toy we wanted around for our kid already when gma previously mentioned this 'great item'. Probably would've been fine with it, had nobody been encouraged to hit people with it, but that was all gram ).
In our case, dh doesn't get along with his mom and care about her feelings as much, so he'd just rather chuck the stuff or fight with the kids about how they shouldn't have gotten it trying to get rid of it later than deal with his mom. Honestly, I have an easier time - my mom completely forgets most things she gives us, and wouldn't really care if the kids had fun covering something in mud, paint, paper mache and then we eventually got rid of it. And I kinda get it from dh's point of view - because he'll try to talk with her, and then she'll go on to do whatever she wants anyway. It might be the case for your dh too? In our case it takes me getting angry/upset/intense about something and stepping and and being all 'NO WAY, NOT FOR MY KIDS' 'But I figured it would be okay because. . .' 'NO WAY, NOT FOR MY KIDS. WE'RE DONE WITH THIS! THANKS ANYWAY! TAKE IT BACK NOW.' (which she gets nervous about) and then she'll remember the message. I cut off and ignore debates about stuff, my standards are not up for debate at the moment around my kids, yk? I've also taken candy right out of my kids mouth, when not asked first about it (I depend on instilling in my kids that they have to ask ME about stuff, since we can't always depend on grandparents to be reasonable. You might need to work on the same, but it's great to have the kids come over to ask me whether they can eat the candy gma just gave them).