According to Merriam Webster the definition of AGNOSTIC is very simple:
1 : a person who holds the view that any ultimate reality (as God) is unknown and probably unknowable; broadly : one who is not committed to believing in either the existence or the nonexistence of God or a god
2 : a person unwilling to commit to an opinion about something <political agnostics>
Now, to use this in a sentence:
Girl du jour is AGNOSTIC. I’ll believe it when I see it.