Yeah, I’ve had That Guy in my game a few times too. Sometimes the only thing a player like that understands is “screw around and find out.” And GURPS is not written around the bizarre idea that PCs should be able to win every fight because it’s encoded into the rules to keep power-tripping munchkins happy.
This scenario assumes medieval fantasy. TL3 overall, the town where it goes down is TL2(3), and there are TL4 neighbors close enough that there are a few high-tech imports floating around, too. These imports specifically include early TL4 guns. The Militia is locally-equipped for ease of logistics, but not everybody who knows how to fight is in the Militia. So when you get to the “dangerous people,” bear in mind a few of them are going to have the TL4 equivalent of a twelve-gauge, a few more will have pistols, and at least one will have a high-powered rifle (for TL4).
In this world, I decided not to use the cliched and boring trope of “orcs evil. Me kill orc for fun and steal his stuff! Everyone love me for it!” Instead, orcs are considered people with rights. There are orc raiders out in the woods, but there are human highwaymen too. If a PC kills an orc and drags her head back to town thinking it’ll impress people, they’ll find out Sheriff Beauregarde and Judge Lakatos aren’t so much impressed as infuriated because Scooter’s been wondering where his wife Lurleen disappeared to and just found her head in the PC’s hand. Yeah, they’ll be “impressed” right up to the point where they pull the lever and give the murderer a short drop to the end of a rope. Assuming the Sheriff can stop Scooter and Lurleen’s fans (they run Scooter’s Barbecue Pit, the best orc barbecue joint for thirty miles in any direction) from tearing the offender apart with their bare hands first.
That’s when you drop him into a town on the bleeding edge of the frontier with Sheriff Cletus Beauregarde.
Cletus is a seven-foot tall 200-point orc Big’un. He’s unshakably honest and utterly incorruptible, basically Judge Dredd, can turn a street gang into chili meat singlehandedly, the townspeople know he’s the living embodiment of the Law, and the local Judge trusts him implicitly. Some Mafioso type tried to buy her off once, then tried to “persuade” her when she laughed in his face. She told Sheriff Beauregarde, and when he brought the Mafioso in, he had so many broken bones his testimony had to be given telepathically. That was nine years ago and nobody has tried it again. If she has to travel, Sheriff Beauregarde is her bodyguard. His reputation for honesty is such that his testimony is considered legal evidence.
If someone offers no real resistance, he takes him or her into custody with minimal force. Suspects who run will be knocked down with his Enforcement Club (small round mace +1 Accuracy and Puissance, Tanglefoot, and a dedicated Powerstone that will power Tanglefoot four times, Limit enchantment so it will only work for the current Sheriff of his town) and grabbed as they get up. Violent resistance usually results in the offenders being beaten unconscious and deposited in the jail with at least one broken bone each. Cletus has no qualms about killing, but he doesn’t see it as his job to kill criminals when bringing them in alive is a viable option.
He’s also a gay bear, and his current boyfriend is a tiny, twinky, human drag queen. Nobody says a word.
When he isn’t with Alexei, he’s usually out in the woods hunting boar for Scooter. In theory he trades the meat he brings home for his tab, but neither of them has bothered to do the math. They each suspect they’re coming out on the short end, but they’ve been good friends for so long they don’t want to make an issue of it.
Here’s where it gets really fun. Remember the Sheriff doesn’t live in a vacuum. As a townsperson of note, he has relationships with a lot of townspeople. As Sheriff, he makes a point to know the dangerous people, either to make sure they behave or to see if they’re willing to help him on occasion. Think six stars in GTA.
On top of all that, he’s a Lieutenant in the Militia, commanding the home defense squad. People think it’s a joke assignment, but he has it because everyone knows he won’t take advantage of the chaos, and neither will his men — they all have Honesty (12) and most have Truthfulness (12 or 15). As last lines of defense in case of an enemy breakthrough go, he and his guys are hard to complain about. And if some idiot comes into town acting like a jackass and tries to take him down, they’ll be facing not just the entire town Militia in general, but his deputy and the home defense squad in particular. Plus every other dangerous person in town. Oh, and the elite Militia Trollhunters — guess what they do for a living.
Those “dangerous people” include all the local bounty hunters (Sheriff Beauregarde deals honestly with them) that happen to be in town. As well as a few independent battle mages and mercenary squads used to hunting Chaos Sorcerers. Yeah, there’s a coven of those building a power base a few days’ ride out of town.
Hell, the Mob is probably going to join in the fun too just on general principle and so they can see if they can leverage their help down the road.
Basically, go through the list of major NPC combatants in town and unofficially deputize the lot of them.
If the munchkin somehow survives, there’s always the very real possibility that the Trollhunters weren’t at full strength. They’ve always got people out in the field. Guess who will be out for blood after something like that goes down. So That Guy will have a squad of the best troops in the area, whose entire job description is “hunt down regenerating ogres that puke nuclear waste and kill every last one of them,” hunting him.
If he’s smart, he’ll head into the ugly part of the frontier so only the Trollhunters will be after him. Which means he’s taking on every creature in a place that even Mordor’s goons won’t go near without serious incentive like “go there or I’m cutting your guts out and eating them while you watch. Then I’ll get mean.”
If he isn’t smart, he’ll figure on heading for another town. That’d work except that Judge Lakatos put a bounty on his head and had it spread telepathically to every town nearby. Guess where else Sheriff Beauregarde has a solid reputation as a good dude all around.
So not only will Cletus and company be able to put up a real fight, but it’ll be humiliating too. Because after the fight is over, he’s getting dragged into court and chained in the dungeons until either he learns to behave himself or one of the local mages (probably an orc Voodoo sorcerer) nails him with a Great Geas that forces him to do so or face some ugly side-effects.