The TVTropes Trope Finder is where you can come to ask questions like "Do we have this one?" and "What's the trope about...?" Trying to rediscover a long lost show or other medium but need a little help? Head to Media Finder and try your luck there. Want to propose a new trope? You should be over at the Trope Launch Pad.
I mean, though, "fanboy bought the company/product" is absolutely a situation that could come up in fiction too.
The first thing coming to mind is Screw the Rules, I Have Money!, but that does fit Musk more than a potentially more benevolent fictional example.
^ Screw the Rules, I Have Money! is supposed to be for using money to get out of trouble or rulebreaking. Deciding to buy a company isn't that kind of trouble.
If we're supposing a fictional situation where someone is throwing enormous amounts of money around for silly reasons, I'd think Conspicuous Consumption or something related like Executive Excess. "Look at me everyone, I can buy a multi-billion dollar company on a whim!"
Edited by KD

Elon Musk liked being the world's richest Twitter troll so much that he bought the company and made himself CEO, and has been, shall we say, very controversial in his new job. Is this Promoted Fanboy, Running the Asylum, or something else?
Edited by Ronfar