When a person thought someone or something was square they would draw the shape of a square with their forefingers in the air (out of sight of the so called "square").
A popular slang term for leaving in the 1950s was "split," as in "Let's split this joint."
"Don't sweat it" was a slang expression in the 1950s that meant "not to worry."
"50 slang" could refer to slang from the 1950s (such as "cool cat" or "greaser") or slang that originated in the area code 50 in Minnesota. More context would be needed to provide a specific answer.
A Yank tank is Australian slang for an extravagent American car, or United States slang to a pre-1950s American car in Cuba.
Australian slang for "good on you", meaning "well done", as in a deed well executed, or as a gesture of encouragement.
Fake Out is 50's slang for a bad datejacketed: dating only one person was also called "going steady".
In North America the 50s ended in 1963 in the opinion of my peers. As our world changed so did the slang.
A square is a person who is not "cool" or "hip." This would be the person who is unpopular and does not follow the latest fashions in clothing, slang, and behavior. "Square" is an old slang term from the 1960's.
Some teenage slang from the 1950s included phrases like "cool it," "cruisin' for a bruisin'," "pad," "threads," and "hot rod." These terms were often used by young people to express approval, warn of potential trouble, refer to a hangout spot, describe clothing, or talk about a fast car.
"Square" is slang for someone who is conventional, boring, or out of touch with current trends or culture. It can also refer to someone who is seen as uncool or doesn't fit in with a particular social group.
In its standard meaning, "moon" is a noun. In vulgar slang, "moon" can also be used as a verb, meaning to make a particular kind of vulgar gesture.
Hip as a slang word means knowledgeable, so clueless or square would be the opposite of the slang. Square means someone who is not cool or hip or does not know the common way of doing things socially.