Hiking is fun until it's not. And it's usually not when you have a massive blister bubbling under your big toe or your backpack rubs the skin on your hips and shoulders raw. None of these are immediately life threatening—unless you don't treat some of them in time—but they're a surefire way to cause serious discomfort. We want to know which ailment would ruin your trip, and if you have a specific experience, share your story with us in the comments.