The phrase 'Take it Easy' is used to say good-bye and be relaxed.
Example of Use: Mary: "Bye-bye." Bill: "See you, Mary. Take it easy."
The origin of the idiom 'take it easy' depends on the context in which the term is used. If you’re going to relax for recreational purposes, you are using the original meaning of the idiom dating back to 1867. If someone is leaving and you’re hoping they have a nice time, you are using a later version of the idiom. If you’re telling someone to 'take it easy' as in “relax, you don’t need to cause a stir,” you’re using an even later version.