Everyone is an alien to someone.
I'm in my late 20s. To anyone under the age of 18 today, I'm from a world they have never been to, and never will. A world we call the 1980s. It was inhabited by creatures with big curly hair that listened to cheesy pop music and grazed on Pixy Stix and Lik-M-Aid Fun Dip (aka sand you can eat). I grew up there; I have vivid memories of the world around me and the formative first experiences I had in it. But anyone under 18, they can only dream of such things.
See, this isn't even the packaging I remember, but it's all I could find on the internet. That old Lik-M-Aid packaging, it's lost to time; it only exists in my memory of that alien world (and maybe partially rotted in an old box in someone's basement).
Space aliens are separated from us by distance; we are separated from other people by time. But really, time is just the distance between two things that happen in the same place.
Which, of course, means that anyone older than me is an alien too. If a little grey man stepped out of a flying saucer that carried him from a planet I could never visit, I'd be treating him like a sort of god, asking him every question I could think of. Maybe elders should be treated with the same respect and reverence.
This isn't limited to time. The subjective experience of any one person can't, by definition, be experienced by other people. To anyone else, it's an alien sensation that can only be indirectly and imperfectly expressed. But even second-hand transmissions from the alien landscape of another person's mind should be fascinating. Indeed, it's what makes conversation with someone new so great. It's what gives mass expressions of one's consciousness - art, music, poetry, writing, whatever - their magic. SETI is cool 'n everything, but Earth's own idiosyncratic aliens are just as fascinating.