Clothing no-no: Low-cut, revealing, unsupported, and light-colored tops
Issues: I have had to tell a woman across from me in a yoga class that her boob fell out of her shirt. Some tops seem like they fit while you're walking around, but they just don't support your ladies once you start moving, especially when doing Down Dog or Headstands. White or light-colored tops are also risky, especially if you know you get pretty sweaty — you signed up for a yoga class, not a wet t-shirt contest.
Do wear: To avoid a nip slip, sport a top that supports your body type. If you're big-busted, a V-neck or lightweight sports bra may not be your best option. Some shirts contain attached shelf-bras, but if they offer minimal support for your girls, you might want to wear a sports bra underneath. Bright colors get the thumbs-up, just make sure they're not see-through.