A: You should be more polite to strangers. You never know who they are.
B: I don't give a dead cuss who you are.
-- A "cuss" is a colloquial form or "curse". "Not to give a cuss" = "not to care". ("Dead" is here an intensifier.)
A: But Ä 160 might jog my memory.
B: I'll be back.
-- "I will return". "Back" is here adverbial "to be back" = "to return".
A: Back already, yeah? Got the money?
-- i.e. "You have returned already? (The speaker acknowledges that B has returned.)
B: Here. Now, how do I find Bouchard?
A: It's not going to be easy y'know.
B: Let me be the judge of that.
-- i.e. "I will decide whether or not it's easy to find Bouchard, not you!"
A: Bouchard has had big trouble lately. And he owes me! Big time!
-- The first part is the present perfect. Bouchard's big trouble began in the past, and continues into the present. "Big time" means "to a great extent", or "very much".
A: I know a password that'd get you past Bouchard's door guard at his new hideout.
-- yes, "that would".
B: You'd better not be giving me the run around old man.
-- "Old man, I hope you are not attempting to deceive me!"
Let me know if it's still unclear!
All the best,
Student or Learner