A Meme that originated from the American tv show 30 Rock. The gag comes from Jack Donaghy's (Alec Baldwin) private investigator, Lenny Wosniak (Steve Buscemi), who claims to have worked in an undercover police task force of youthful looking cops that infiltrate high schools, a reference to the popular cop show, 21 Jump Street, which featured a young Johnny Depp. However, when the audience sees a flashback of Wosniak undercover at a high school, he tries to blend in by saying "How do you do fellow kids?" to a group of high schoolers, who aren't fooled since Wosniak is too old to look like a teenager.
The meme has since been used to joke about older people that try and fail to sound hip with modern youths.