As a layman, it looks like failures to deliver have very little consequence, so I'll ask some stupid questions here. If one of these activist investors happene

As a layman, it looks like failures to deliver have very little consequence, so I'll ask some stupid questions here. If one of these activist investors happened to have lent a stock out, which then failed to deliver, what is the worst consequence they could inflict on the borrower? If no consequences are available, then how do short squeezes happen?