comes from a slang-language in the beautiful state of Hawaii called "Pigeon-English".
definition: safe - adjective used to describe silliness, stupidity, or ignorance.
Sometimes used in extreme sarcasm! Like "DUH!"
"Wow! Dat guy wuz so safe, he couldn't even count da change, brah!"
"My little braddah, he act so safe. He 35 years old and he act like one 2 year old!"
"I going to da store fo' one beer. You like one?"
response: "Well, yeah, safe!"