What does the phrase "I'm knackered" mean?

John: "Excuse me, could you tell me where the loo is please?"
Waiter: "Of course, just down the hall and then to the right."
John: "Thanks"
Where is John asking for directions to?

What is the informal name for a five pound(£) note?

A blue note (because five pound notes are blue)

What does the idiom "the bee's knees" mean?
Examples: "You look the bee's knees!" 
                    

Julia: "Don't cry over spilt milk, Victoria it'll all be okay."
Victoria: "You're right, I'm just a bit cheesed off today."
What do the idioms "Don't cry over spilt milk" and "To be cheesed off mean" ?
(Note: These two idioms do not have to be used together)

(Don't get upset over something unimportant) (To be out of energy)

(Don't get upset over something unimportant) (To be angry/frustrated)

(Don't forget to put the lid on the milk bottle) (To feel confused)