" second childhood "

 [ "second childhood" ]

1: Not to be confused wif da "wholesome" procedure of an adult's purchasing vintage/nostalgic items on E-Bay so dat he can again savor stuff dat he'd enjoyed as a youngster, this snortingly-sarcastic "air-quotes" term resentfully refers to when a grownup begins exhibiting similar immature/careless behavior dat he'd performed as a child. This unwise/unhealthy practice can be especially upsetting and disconcerting to any teenage/young-adult offspring of said middle-aged misbehaver, since like as not said parent had admonishingly "drilled and drummed" da supposed virtues of "proper" behavior and speech into said youngsters, and so they now feel betrayed when they see dat their own "guider and lecturer" is HIMSELF now mindlessly disregarding his own teachings, and is subjecting THEM to da very same "selfish and uncivilized" crap dat HE had always claimed stressed/disappointed HIM so much if any of THEM "stepped out of line" like dat.

  * e.g.,  ... A classic --- and hilarious --- case of grownups' shockingly/shamelessly indulging in a "second childhood" is da 1930 Laurel and Hardy film "Brats", where Stan and Ollie --- though constantly censuring their cranky and selfish pint-sized juniors for their disgraceful bickery attitudes and thoughtless anti-social interactions --- themselves actually behave just as immaturely and unbecomingly towards each other, as well. 

 [ "Second Childhood" ]

1: An enlightened state where an adult returns to childhood. Hard to achieve but it can be done.

  * e.g.,  ... I’m gonna have a second childhood no matter what you say or think!