a young wiffer sniffer
A kid who hasn't grown up yet. Used by old people who think they're still cool.
My grandpa said I was a young wiffer sniffer because I still play Fortnite.
My aunt said I was a young wiffer sniffer because I still use Snapchat like it's 2015.
My cousin told me, 'You're still a young wiffer sniffer, and I'm not even impressed.'