This was a series of events told to me by a Tumblr-less friend to post here. Necessary context: a dragonborn rogue, in spite of his class and proficiencies, has a love of fighting with a greatsword - specifically, a unique one picked up a few sessions in that has an undercommon phrase engraved on it that none of the players can read. One session, he goes ahead of his party to investigate in a mansion, and comes across another greatsword hanging on the wall, which has the same phrase written on it.
Rogue: Hey, that’s my sword!
DM: Well, a copy of your sword, basically, yeah.
Rogue: I refuse to share my sword with anyone! I want to sue whoever owns this sword.
DM: That’s not-
Rogue: I ROLL TO SUE.
DM: You don’t even know who… you know what, fine. Roll Charisma with disadvantage.
Rogue rolls. Lowest roll is a 21.
DM: …you track down the owner of the sword, a veteran fighter, and sue him. The case is taken to court. Roll for how well your lawyer does.
Rogue, laughing, rolls a nat 20.
DM: (having gone from annoyed to greatly entertained) Alright, you perform a ritual and summon Phoenix Wright from another dimension, and he successfully gets the veteran declared guilty of plagiarism. All this took about a week. You receive 1500 gold in “damages” and finally return to the mansion, where the rest of your party has been impatiently waiting to continue your quest.
Other party member: I punch him in the face. (rolls, hits)
Rogue: Can I roll to sue for assault? (everyone glares at him) …I take the damage.