Being a Christian is not claiming to be Christ. Claiming to be a Jedi, however, is making a claim to be able to use the Force.If someone claimed to be a Jedi to get some sort of special consideration, I, if I was in the position of authority, would kindly ask them to move an object using the Force. If they failed to do so, repercussions would ensue.
I'm just curious: should we apply the same test to, say, Catholics? Transubstantiate this cracker into the literal body of Christ, or I won't believe you're really a member of the church. For Jews, give them a small oil lantern and ask them to make it burn for eight days. And I'm sure we can come up with similar demonstrations of supernatural intervention from every faith tradition before we accept their beliefs as a legitimate reason to take a day off.
Or we can agree as a society to take all claims of faith at their face value, especially when it comes to something as trivial as a parentally-sanctioned vacation day.
Claiming to be a member of the Jedi Church is distinct from claiming to be a Jedi as portrayed in the movies. See their website for more information.