When you're in bed with regulators, everything is possible. Of course normal people can't do it (as it should be).

Borrow a share. Sell it. Borrow the same share. Sell it again.

Borrow a share, then let someone else borrow it from you.

Normally, when you short a share, your broker has to go find somebody who already owns it and they "borrow" it from there and allow you to "sell" it short. But if you can believe this, the very, very largest Wall Street firms, (Citadel, Sigma2, etc.) those with trillion dollar balance sheets got a special exemption from the SEC : rather than having to "find" shares to borrow, they can "manufacture" shares, using their massive balance sheets as collateral. This is how 140% of GameStonk can be shorted. It is this unfair playing field that r/wallstreetbets is fighting against. Since the short exceeds the float, it is possible that there could be an "infinite" short squeeze, that even if they took the company private by buying every available share, there would still be another 40% outstanding they would have to cover. HOLD!

A has 1 share of GME.

B borrowed it from A and sell to C.

C has 1 share of GME.

See, magically, A and C has 1 share of GME each.

For example Gamestop could've issued and sold new shares, instead they were forced to wait or sell them for unrealistic price.