Sometimes, when you're in a wet bikini, a breeze may come along and whip your nips to a point. If you hate it when this happens and turn red from the pointing, there are suits designed to help avoid the embarrassment.
The first line of defense is simply a lined suit. This can be a liner like what you'd find in a dress or jacket and works the same way. Or it can be a double-sided or reversible suit with another layer of swimsuit fabric. Simply looking for a swimsuit with an extra layer of material will help provide a bit of a shield.
Another suggestion is to find a suit with some padding. It works the same magic that a padded bra does and helps to maintain a smooth look. Some suits are lightly lined while others have some push-up padding. How much you want is up to you.
If you don't like the extra heft that comes with a padded bikini, wearing a print is also a great option. A busy pattern helps to camouflage any unwanted pointing. Darker colors are also helpful as well.