There are so many freaking great lines in this show.

"You'll hang for this!"
"Seven years serving you? I deserve worse than that." That dude was just one of the best characters I've seen in Star Wars, with minimal screen time.

"What about your brother?"
"I don't have a brother" - I love this because we (and Cassian) don't even know what it means, my first take was literally that he made up the brother story and that's probably right. But it could also mean that his brother is dead just like he said in his story, and all that matters his him looking out for himself.