I've heard that some FFLs reject anyone who checks the non-binary gender box that the woke ATF added to the 4473 because checking that box is proof of mental illness. Legally, an FFL can deny a sale for any reason, and there is very little chance of another Masterpiece Cake Shop situation as no judge wants to rule that a gun store owner violated the Civil Rights Act by refusing a sale because he felt something was off about a potential buyer because they'd be blamed for the next mass shooting.
In case you think I'm joking, the ATF really did add a "Non-Binary" box to the question asking you to check your sex:
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