Someone who studies the art and science of yapping intensively; someone who yaps a lot to the point where they know much of the science and art of yapping.
Someone (usually one with authority) who is exceptionally skilled at yapping and boring anyone out, evenpeople with the best attention spans. They usually have something important to talk about, and usually end up speaking about something way off topic.
He's such a yappologist - he will turn any 10-second explanation into a full blown TED talk.
Stellen: I'm so gay my bitch is gay yada yada yada yada booga booga boo
Jackson: Stfu you Yapologist
Stellen: you best quit yapping before I suck your dick