13. Flip-flops: Experts say that flip-flops expose your feet to all the gross things: bacteria, viruses, and fungi that can trigger an infection if you have so much as a hangnail or a microscopic skin tear and a not-so-top-notch immune system. On top of that, your sorry excuse for sandals can cause heel pain, disfigure your toes, and affect your posture to trigger a host of other aches and pains. So save your flip-flops for the gym shower and pool deck, and rely on more supportive footwear to take you everywhere else.