A bit related - I've seen forums etc. where the community pumps stocks, crypto currencies, and what not.
Everyone knows what happening, and they're all in on it.
One typical way is that some "stock guru" is selling spots for private chats / rooms, where they'll regularly announce "signals" - i.e hyping up some penny stock. The group members will obviously start purchasing shares / pumping the stock, and exit as soon as outside buyers enter the cycle.
Sometimes they just flat-out announce public pumping schemes on forums / user groups.
The thing with Hertz' stock going crazy even though they declared bankruptcy was insane... people were buying the stock because they're betting there'll be another idiot wanting to buy the stocks off them for a higher price. Which is the entire principle of crypto, IMO.