Like a Grammar Nazi, but someone who goes crazy when a person uses a filler, such as 'um', during a conversation, even when that person is totally unprepared to speak.
Teacher: Billy, come to the front of the class and give a 5 minute speech on the last book you read.
Billy: The last book I read was...um...
Teacher: TOO MANY FILLERS!!!
Billy: Sorry. So, I was saying that-
Teacher: BILLY, SO IS A FILLER! NO FILLERS IN MY CLASS!!!!!
Student 2: Damn, what a Filler Nazi...