I know gifting - the giving and receiving of gifts is a hot topic that creates lots of angst.
My mil decided that since she loves to collect knick knacks, that I should too. Since I love cats, she started to give me 'cat' gifts for my birthday, Christmas etc. I got figurines, pictures, bags, mugs you name it. I asked xdh to talk to his mum, but that never happened. I finally had to sit her down and say I appreciate the thought, but I love live cats, not images of cats. I asked her not to give me gifts, I do not need 'stuff', but that did not work. I asked her to give in my name to the local cat rescue, but donating if foreign to that family. Finally we settled on her taking me out for lunch.
If I were you, the next time someone tries to give you a bag of fabric, say 'Thanks for thinking of me, but I cannot use it, how about giving it to (give them the name of a group who makes charity quilts, a school that still teaches home ec etc)'
If it is a pattern, tell them you are only working on one project at a time and need to stay focused.
If someone offers you their Auntie's stash, think about what you could do with the fabrics from 40 or 50 years ago? I am not yet 50 and have a 30 year old fabric stash. If I have not purged the wild 80's prints would you want to? You can always use space issues to avoid another person's stash.
Lots of people here will say make charity quilts with the fabric you do not want. Now what I am going to say will not sit well with everyone but here goes.
Not all of us have the time, even if we have the resources donated to us, to make charity quilts. My sewing hours are limited, I do not have enough time to do the projects I want to do in a timely manner. If I feel obligated to sew for charity because someone gave me a bunch of fabric I did not want or need I am going to feel resentment, not the joy of giving to others.
Now having said that I do personally participate in charity quilts through my Guild. We do them as a group project and I helped out all day yesterday to prepare 11.75 quilt tops. I brought the unfinished one home to complete. We will have another sew day to complete the quilting next month.
It is okay to say no thank you.