In my friend group there were a handful of specific blunders that significantly changed the tide of opinion against him, all around the 2018 timeframe. "Pedo guy" was the biggest one mostly because of how stupid and unnecessary it was and his unwillingness to back down, but the "taking Tesla private for $420/share" drama was a close second.
The increasingly pubic tawdriness of his love life was a factor too; prior to then he'd done a good job cultivating an image of a family man.
Specifically on Reddit I've never seen anybody support him anywhere near what one could consider "faboyism". They have this funny feedback loop where there's a (usually negative, or only marginally relevant) Musk post on the front page at least once a week, and the comments are all about how they hate Musk and how people need to stop giving him attention. Somehow everybody is completely oblivious to the fact that these posts are the only ones that most people ever see.
And about 1 in 4 or so care.