My little kobold multi-class disaster (currently draconic sorcerer 5, bard 2, fiend warlock 4) has Yeenoghu, the demon god of destruction and gnolls, as his patron.

I don't think Yeenoghu was looking for warlocks. My kobold was just a sorcerer and maybe 1 level in bard in a Westmarches style campaign. Early on we kept running into various Baphomet cultists, then during a random encounter got caught between two gnoll factions; one still loyal to Yeenoghu and traitors who switched to Baphomet.

High charisma and one single gnoll caster who could speak common and we were able to negotiate a truce with the Yeenoghu group and a reward if we recovered some gems that were stolen by the Baphomet group.

Got tired of constantly running into Baphomet followers everywhere, so my little guy went to his gnoll allies and was like "Hey, we hate Baphomet and your guy hates Baphomet, would he help us if we help fight Baphomet's followers?"

He doesn't fully realize the extent of a warlock pact (8 INT and 12 WIS) . He thinks we're just allies and Yeenoghu is giving the power with nothing in exchange except killing Baphomet cultists. Even though we haven't encountered any recently. Even after he developed this unquenchable hunger for flesh and blood. Even after his alignment got knocked from chaotic neutral to chaotic evil when he started gathering parts and trophies from humanoids we'd killed for an altar in his tower. Even after he was given a "blessing" that was horribly painful and turned his little kobold teeth into larger, more gnoll-like fangs.

My multiclass Lizardfolk "Great Old One" Warlock 7, Paladin Oath of Vengeance 3 and Ranger Hunter 3 has the Platylord, an omniscient being resembling a platypus that hates dream eaters, as his patron.

My Lizardfolk (Jugular) began his study of the Platylord when he first saw a platypus swimming around in a river by his homeland. He uncovered the secrets of his patron through extensive study in a local town (which, surprisingly, appeared empty whenever he came by*). The Platylord decided to acknowledge his existence by granting him powers. Later on in the campaign, when Jugular saw a Platypus be killed by a rampaging Aboleth, he swore revenge and leveled up his a Ranger (favored enemy: aberrations) and Paladin levels and later on killed the aboleth.

*This was in no way involved with the time he "accidentally" bit someone's tasty, tender, delicious arm off.

I also had a "Great Old One" Warlock 5 and Paladin oath of conquest who's patron and deity he worshipped was Xanathar.

My player made a deal with a group of mindflayers so now he's a part of the hivemind and is trying to further the great design. I also named the mindflayers after single letters to save myself the time.

I knew someone who played as Leonardo Da Vinci, and had his patron be "The Arts"

As for me I have a Warlock who's the avatar of death, and thus draws his power from himself.

Flying Spaghetti Monster.