I don't think you understand what troll stands for.
You were incorrect when you said "Its definitely not a fraction of fast food costs", when labor cost is. A fraction is a mathematical construct. By definition the labor cost has to be a fraction of the total cost of the burger.
You are confusing the relative size of said fraction to other contributions. But he never insinuated as to big or small fraction of labor cost. And when you replied, you really meant to say "definitely not a small fraction of fast food cost", but he never made such insinuations about big or small contributions, and you never said big or small fraction yourself. So that is why I pointed out you are wrong, because labor cost most certainly is a fraction of the total cost.