The pseudo- prefix means fake or spurious, so a pseudo-Christian would be someone who fakes it, pretends to be a Christian, presumably for some non-religious purpose, like being accepted as a member of a community.
It could also be applied to people who believe themselves to be Christian but don't actually understand the faith's teachings and thus malpractice it. Pat Robertson, Jerry Falwell, and that prehistoric Pope Rat Zinger come to mind.
And then there's Five Pair o' Ducks there, who's declined to tell us what he thinks it means. :lol: Maybe the word you want, FP, is parachristian...