My main pet peeve is being interrupted by family members when I am sewing. I don't get much time to sew and when I do, I guard it like a dragon does treasure. I get an endless stream of interruptions and usually they are at a critical moment of stitching or cutting and I HATE that! (how do you kindly tell your five year old to get lost??)
I guess after that, my other main pet peeve would be making careless errors. It is one thing to do something wrong because I don't know better, but man does it bug me when I DO know better and still goof up!!