it took me a while to figure this one out - I have a lot of annoying habits, but one that I wish I didn't have? which of my habits hinder my ever day living to the extent that I wish I didn't have it? of course, most bad habits you wish you didn't have, but it's not the end of the world. take biting nails for instance. if I'm not biting my nails, I'm biting the skin around my nails but my nails always grow back and my skin eventually heals. so I don't find it that big of a deal.
I guess what bothers me the most - and you may find it gross - but the habit I wish I could stop is picking at pimples/zits/blackheads/whiteheads/bumps. it doesn't help when all the women in my family also do it and almost encourage it (hey, let me get that mountain on your forehead!). it takes physical effort for me not to pick at my face. and I don't have serious acne issues, but since I pick at my face so much I tend to scar and make those suckers worse.
check out the full list of challenge-ness here.