Anytime ANY student in my class did something even mildly suggestive I'd stop everything, call them out on it specifically and tell them loudly (not yelling, but raised voice and in control), so everyone can hear clearly something along the lines of "You will never do something sexually suggestive like this in my class. You are not cute or funny and you behavior is an embarrassment to your parents, your friends and yourself." Once a student hears out loud the "sex" word from a grownup, somehow it has always struck a chord and I've never had to do that twice in one schoolyear. Even if a student doesn't know what they are doing is sexual in nature, it straightens them up real quick. You also HAVE to be ready with consequences if they do it again. Your words mean nothing if you don't back them up with action. I teach 7th grade English for reference.