Wild shit eh? What do you think JN means to a judge? It means the potential jurist is defying court direction and doing so out loud in front of everyone. It is by definition contempt. You do not get to say "I will flout your instructions and ignore the law and everyone of my peers next to me should do the same" and expect an 'okay then, have a nice day'.
To vote your conscience as an actual juror, and convince others to go along with you during deliberations is absolutely legal. Telling the law to fuck off in official sounding language prior to being an actual juror is not, and that is essentially what the statement "I support JN" is doing.
This whole idea that there's this 1 easy trick to getting out of jury duty is a myth born from a gross misinterpretation of what actually happens vs what it sounds like should happen. Will you get out of jury duty eventually? Probably. Will it be as easy as whipping out your "I know JN exists" membership card? No way.
Please, while we're talking 'wild shit'. Explain what you think will happen when you say "I support JN so can I please be excused?" and the judge spins, glares at you, and turns 3 shades of red. Before you answer that, this is a judge's response to a nurse simply saying she would be biased due to her experiences related to the case in question. She actually had direct, relevant reasons to say she would be likely to nullify in one direction or the other and wasn't simply saying "muh, JN, seeya".