A conversationalist is someone who likes to chat, and is good at it. Conversationalists love to have — surprise! — conversations.
If you’re seated at a long formal dinner party, you hope the person next to you is a great conversationalist or you’re in for a long night. A great conversationalist will tell you interesting things and probably make you laugh. For a conversationalist, chatting and bantering come easily. A conversationalist is witty and clever, like Dorothy Parker. A bad conversationalist would say inappropriate things, like tell you about an infection just as you’re taking a bite of mashed potatoes.