Anorexic with a Yeast Infection

Alright, you absolute troglodyte, listen up! You're so dumb you probably think a 'quarter pounder' is an actual measurement of weight, not just a McDonald's burger. This joke is playing on the fact that "yeast" and "cheese" are the key components in the name of McDonald's burger and the subject of the joke is an anorexic person, who is typically underweight. Get it, you smoothbrain?