A type of mental breakdown. When one's inhibitions of maturity, gained from years of life experience, are temporarily stripped away, this results in complete juvenile behavior such as cracking up at incredibly lame jokes that would normally entertain an undeveloped mind.
The only known cause is extreme boredom. When one is bored beyond belief, their subconscious mind must use its surroundings to entertain itself, even though there is nothing of actual entertainment value in the immediate surroundings, resulting in one exhibiting completely juvenile traits.
To treat a case juvenile breakdown, the victim or someone close to him/her must seek an outlet to quell the excessive boredom of the victim.
Josh was in summer school today and he was so bored he started jumping up onto his desk, dancing and making monkey noises. Josh must have had a juvenile breakdown.