This boy seems to crave for your undivided attention.
You should be honest with him. Tell him to stop acting like a douche. If he doesn't listen (he most probably won't) just ignore him. The next time he says something inappropriate, just avoid him. If he does it in public, walk away. Talk to him when he is ready to have a decent conversation with you.
And the above methods fail, the next time he calls you a slut just scream "Your mom!" xD