When I walk in your store, do not come up to me and ask me if I need help. Considering I walked straight to the yarn I want and am grabbing several balls, I think I know what I'm doing. If this is your standard response to people who walk in the store, fine. If so, you might as well ask other people in the store if they need help as well. I saw you avoid that old lady.
Do not treat me like I know nothing about yarn. If I ask for sport weight yarn, do not show me dk or worsted weight yarn and try to pass it off for sport weight.
If I ask for wool, do not show me cotton, alpaca or *shudder* acrylic blends and tell me they knit up similarly.
Yarn store employee, do not ask me if I know what gauge is. I asked for sport weight. I think I know what gauge is. Oh, and when I say yes, do not then explain to me how the yarn you're holding knits 6 stitches per inch and tell me exactly what that means.
Please do not assume I'm knitting a scarf. There's nothing wrong with scarves if that's what pleases you, but I think it's safe to say if I'm buying 6 balls of an alpaca blend and some size 3 needles, I am not knitting a scarf. (By the way, don't you remember me from Christmas when I almost bought out your Mega Boots yarn? For socks??)
Do not look at me blankly when I tell you I am using an Elizabeth Zimmermann pattern. This is particularly embarassing for you, since you're standing in front of several Elizabeth Zimmermann books. And you sell them.
Do you treat me this way just because I look young? If so, are you under the impression young people cannot knit more than rectangular garter stitch? If so, you are wrong. DEAD WRONG.
Yarn store shopper