People who leave worthless comments on webpages.
I was recently helping my sister hunt down instructions for a specific DIY home project. She wanted to take up Underwater Basket Weaving. Currently, Freshwater Basket Weaving is very popular and there is a ton of information available to help someone get started. However, my sister needed help with Seawater Basket Weaving. After a very tiresome, frustrating search process, she finally found a website devoted exclusively to the study of SBW. Yay! In reading the comments on the page, though, she came across this gem - "I love, love, love baskets, and want to learn UBW! But, I really need instructions on FBW, not SBW. Can you change your page to have FBW instructions?"