Everyone goes bananas once in a while, and everyone, from the youngest children to the oldest oldsters, knows what it means. This fact would not seem so strange except that the expression is practically a newborn babe in the wonderful world of idiomatic expressions. Many expressions are so old that linguists can’t tell for certain even what century they were coined, but a handful of others, including "going bananas," have left a trail of crumbs directly to the source. To go bananas by jumping up and down, yelling, or otherwise becoming overexcited didn’t officially make the scene until 1968.
Language is constantly changing, both in terms of grammar and word usage. Idioms, otherwise known as expressions or phrases, are especially malleable, perhaps because, by their very nature, they belong to folk tradition and are therefore outside the purview of academicians except as objects of study. There’s nothing surprising about a new idiom entering the linguistic stream. What’s enough to make a linguist go bananas, however, is when a new one sticks around long enough to matter.
Cultural changes might not always be traceable to college students, but there’s no question that they are a sort of canary in the mineshaft. Undergraduates are often the first to pick up on and popularize a linguistic shift because it is, in a word, hip, hot, or fresh. Students go out of their way to mine conversations taking place in the street and glory in what they discover.
The expression "go bananas" is one such discovery, but this time, it’s likely the students were making reference to their own histories. The 1960s and 1970s were a time of experimentation. Kids pushed every envelope they could find from conventional love to religion and from religion to ethics. Every expectation inherited from a previous generation became a question, and it was enough to make them go bananas.
That might have been because, in certain circles, they were smoking them — banana skins, that is. Or maybe they really weren’t and only said they were. At the end of the day, it amounted to the same thing. The word spread, and going bananas was where it was at.
Gossip had it that toasting and smoking a banana peel was a cheap trip like that offered by magic mushrooms. This ultimately proved false, much to the disappointment of green grocers everywhere who hoped their retirements were guaranteed. Be that as it may, the rumor at least made a linguistic contribution that continues to this day.