The thing about the fair folk is… they’re not nice. They have unfathomable power and a moral code that’s entirely alien to humans. One that makes their retribution very disproportionate to the insult they perceived.
Some classic examples of what happens when you cross fae are being trapped in a fairy ring.
Being made part of their forest.
Uncontrollable, bestial transformations
Or just straight up being kidnapped and made to serve them until they feel your debt is paid.