I’ll go first.
A person seeks out a fey to get a warlock pact. The person doesn’t know, however, that they’re a sorcerer with strong fey ancestry that just hasn’t manifested yet. The fey obviously agrees to the “pact” and makes a ridiculous contract that the person agrees to. The person lives their entire life believing they’re a warlock when they’re actually a sorcerer. The only thing the fey did was help the person’s magicky shit manifest.
My undead warlock was a graverobber in the business of stealing and selling ancient artifacts. In an ancient tomb that had already been looted, he unearthed an ancient slab and unknowingly released its curse, and is now possessed by the mummy it previously belonged to.
They made a deal and, if he helps the mummy retrieve all the missing artifacts from its tomb, including the body itself, he gets to live (and show off his sick powers).
The first few sessions, his patron was like: Return the slab… and he would refuse out of stubborness, but now they are good pals. Although he secretly plans on stealing his patron’s powers and become the lord of undeath.