If you have a Y chromosome you are a boy.
Home fun telling someone with CAIS (Complete Androgen Insensitivity Syndrome) this.... Especially if they are conservative....
I am sure Susan and Michelle and Cindy will just think you are just awesome and helpful calling them a Boy.....
Only a sith deals in absolutes.
Transgender is a choice, medical anomaly is a fact.
I understand you meant to say "Have fun . . . ". I do find it interesting that you selected a disorder which is so rare as to exist in 5e-5% of the population to 1.010101e-5% of the population. In other words, this condition is so rare that science cannot even predict the percentage of the population in which it occurs. As for causes? Science can tell for what reason this deformity occurs, but is unable to explain why. There are all types of environmental factors which could contribute, all of which have NOTHING to do with God's design.