Kids do like fences with our shit: they pick it
He’s most likely saying kids choose to buy their music. “pick it” and “picket” are homonyms, so the joke is that when he says “pick it” he’s talking about a picket fence, a popular type of wooden fence in mid-20th century suburban America that has become a metanym for the wholesome ideals of the era.
“Picketing” is also a term for a non-violent group protest (typically with homemade “picket signs”), such as striking union workers picketing outside their place of business to draw attention and dissuade non-strikers from going to work. Heems is punning the term with the phrase “white picket fences.” In other words, the joke is that all these protesting kids picket so much that they resemble a whole damn white picket fence.
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