OhTom DeLonge, the former lead guitarist & singer of Blink-182, is a good one. When Blink-182 broke up in 2005, he started up Angels & Airwaves, got a huge head about it, and talked it up like the music they play is "by a band meant to be the absolute biggest band in the world":
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Surprise surprise, it turned out to be an extremely pretentious emo band.
But later on, his real obsession slowly started to come out. Aliens. Specifically, if the U.S. government really has had contact with alien life, and if they're being held captive somewhere. Remember the song, Aliens Exist, from Enema of the State? Yep, you can take that song seriously.
His Joe Rogan interview is a hell of a lot of him going "I know a guy who knows a guy who-" and "I can't tell you that", currently sitting at 27k upvotes, 8k downvotes:
He even made an appearance in the leaked Podesta emails, where he was digging to find info about, you guessed it, aliens.