Haha. I have no problem with material aliens if they actually exist. The problem I have, of course, is people asserting they do in this universe when the aggregate of the evidence asserts otherwise with the negative position becoming stronger as time goes on and science advances.
Of course, as Christians we know spirit beings exist (both good and evil). And we can speculate that other universes might exist in which material aliens exist. But that's where we are at present.
Which, of course, suggests that your neighbor is crazier than a bess bug.
I have one of those down the street though. Get this, he says (with a straight face) that Hitler lives in the center of the earth and is building an army to take over the world. *rolls eyes.*