I always say, "Oh sure I'd be happy to teach you how to do it!" Acting like I've completely misunderstood what they meant. My philosophy is that I will make the time to teach them how, but I won't spend my time doing it for them unless they plan on sitting and keeping me company. The one exception being my Mother-in-Law or my Aunt, they do a lot to help us out in different ways, so I don't mind (too much) doing it for them.