This is a story from my first ever party. We were playing pathfinder with a group of people. The group was initially started by my cousin, who had invited me. It featured a DM who he had befriended at reddit meetups, the DM's brother, another of the DM's friends, and finally my cousin's friend and the topic of this story, who I'll refer by his character name… Mark. I was the youngest person there by far, having just turned 20. My cousin, the next youngest was 25 and the rest were older still.
We initially all met at a local tabletop bar, to discuss rules and get to know eachother. The DM was a real vet and knew his stuff, and I would honestly say he's still my favorite DM to date. Regardless, we were playing pathfinder which has a good deal of rules bloat as is, so his only requests were that we didn't use any 3rd party material for our characters unless he offered it, we didn't use gunpowder as a crutch, and we didn't meta-game. My cousin wanted to play a minotaur so the DM offered to try and find a solution since there wasnt any minotaur race in 1st party pathfinder. We all left excited to build our characters.
In the end, I played an Undine Watersinger Bard named Nyl'Dani, exiled from her village due to being born marked with an omen of disaster, and we were all playing well thought out fantasy characters with extensive backgrounds. Tharn the Minotaur Barbarian, an escaped slave and now free to free others, Moonchaser the Half-Elf Rogue-Cleric, on a quest to find his father on the sea vessel he was named after, Seanut the Dwarf Gunslinger a dwarf in search of adventure and booze… and then there was Mark.
Mark's story was that he was an engineer who lost his job. That was it. No actual reason as to why he was adventuring after losing his job. He just… was. And yeah, the straight man character can be a good gag, this wasn't for a gag. Mark(player) wasn't playing it cheeky or funny, or making deliberate actions to play a character. He just wanted to play an engineer, and Mark sounds like an engineer's name. Which lead to an additional problem, since there is no "engineer" class in pathfinder. The DM initially gave him ideas of playing a cleric of a god of the forge, or a rogue with an emphasis on crafting. Mark rejected all of these because they weren't "engineers". So the DM went into the 3rd party rulebooks to find something, and came back with the Machinesmith, a cool utility caster with some suped up items. Well that wasn't good enough for Mark, because it was called "Machinesmith" and not "Engineer". The DM gave him an ultimatum, that this was the closest that Mark would get to an engineer, or he could play elsewhere. Mark agreed but only if the DM would print the materials for him. The DM agreed.
We began playing and our first session was a mixed bag. We were playing in an empty room at a nearby university campus. Mark did absolutely nothing to make his character in advance so we had to spend the majority of our time showing him how to make his character. We got to play a brief session which we absolutely wrecked face. The DM to make Mark happy gave him a 5 bolt repeater crossbow that was turbocharged by his Machinesmith class feature. The thing was broken as hell at level 3 (which we started at to speed things up), and he one shotted one of the Sahuagin we fought. The Gunslinger rolled a nat 20 to one shot another, and the rogue and I killed another together. The DM was actually a little disapointed at how easily we handled ourselves
The next session, the DM made sure we had enough time to get some action in, and made sure we had a challenge. Session 2 he threw a level 5 hydra at us. This led to the start of our understand of how little Mark understood about the game or about engineers. On his turn, for his standard action he wanted to build a ballista. The DM looked at him in confusion, asking "What do you mean?"
"I want to build a ballista."
"You can't. A round of combat lasts 6 seconds, you have no materials, and you are level 3."
"But I'm an engineer. Why can't I?"
This went on for some time. But needless to say, the DM denied any request to make something stupid like that. Mark ended up deciding to cast a spell, flaming sphere, which he didn't actually know what it did since he never actually looked at the books. Turns out it's a fairly high DPS spell that is one of the only damaging spells in his almost entirely utility-focused class's spell list. It also became the only spell he would ever actually cast.