actually, that one I can explain.
In whole, this quote is part of 'Yankee Doodle' which was written by the British during the revolutionary war. 'Yankee' meaning the colonists, and 'doodle' as an old phrase meaning 'foolish' or 'dumb'
Now, 'macaroni' is an old phrase meaning 'stylish' or 'trendy'
The intention is to say that he was foolishly stating that the feather he stuck in his hat was stylish.
L is not REALLY justice. It is just a clever repetitive metaphor.
However I would like to point out that I really AM justice, and am therefore more smarterer than him.