Of course, your first reaction is “I don’t” and you are likely right.
You are also likely wrong.
Rh negative people, for the most part, are more confused than the general public and part of that has to do with how far removed one’s life is from one’s nature.
Being Rh- has nothing to do with aliens, but telling someone who’s self esteem is already based on such false identity is similar to critiquing a religious fundamentalist or taking the stash from a heroine addict.