It came after President Obama's Oval Office address, during which he advocated for excluding people on the government's no-fly list from buying weapons.
The point of the joke -- which I very quickly realized was lost on some, making it a bad joke -- was that the no-fly list is a secret list that uses secret criteria to determine who finds a home on it. So if you link banning guns to the no-fly list, the scenario presented is completely feasible: The government could theoretically add anyone it wants to the no-fly list, even broad categories of people, and thereby prevent them from owning a gun.
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