Just because you've seen one of those demonstrations with a banana doesn't mean you know how to use a condom, says sex educator Judith Steinhart. It takes practice to get it right, so she advises rehearsing when you have some privacy—and maybe even masturbating with one on. Also: Don't put it on like a sock. Unroll it instead, so that there's a little bit of space at the tip to catch the ejaculate.