The term "peace outside" is a derivative of "peace out" and "peace", all meaning goodbye. It started in the 1960s when the hippies would bid each other farewell by saying "peace" and "peace out". Decades later, the hardcore rapping community and "AZN Ghettos" find "peace out" to be too moderate and mainstream. Therefore they came up with the alternative phrase "peace outside."
Most Asian Americans say "peace outside" to wrap up Instant Messenging dialogues. It's best for the first person to say "peace" and the second person to follow up with "outside" as a gesture of AZN coolness.
The Spanish equivalent of "peace outside" is "paz afuera."
A: I gtg, peace