https://www.law.cornell.edu/uscode/text/18/1001 https://www.law.cornell.edu/uscode/text/18/1001 It has to be "knowingly and willfully", "in any matter within t

https://www.law.cornell.edu/uscode/text/18/1001 https://www.law.cornell.edu/uscode/text/18/1001 It has to be "knowingly and willfully", "in any matter within the jurisdiction" of the government. While this is much broader than most people might realize or expect, it probably doesn't extend to using a nickname in a conversation when the agent hasn't asked you your legal name as part of an investigation! (But the breadth of this kind of rule is definitely a reason that people are discouraged from consenting to an interview with law enforcement without a lawyer present.)