You're going to fight a duel- what weapon do you choose?

My weapon of choice would be frisbees with razor-sharp edges. My disc golf and Ultimate experience would give me an easy win.

I’m intrigued by this. What’s the backstory?

Any mental powers you can wield.

We’ll stare at each other until we get bored. Or he’ll strain so hard trying to kill me that he has a stroke.

Your opponent may use his mental powers to will one foot in front of the other, moving towards you, then will fists into nose, thumbs into eyes, or hands around throat.

“You sunk my battleship” – Bill and Ted

16-ton weights.

I’ll even let the other guy go first.

And I carried one once, as far as you know, so it’s legal.

Pump action shotguns.

If I’m fighting I’m fighting to win. I’m assuming the other person will be an average person who knows enough to pull the trigger and fire but may not be the fastest on the draw or pump. Unless I’m fighting a championship shotgun marksman I think I can aim fast enough to win (and with a shotgun you don’t have to aim as carefully for obvious reasons) plus with the rules a single shotgun blast to the torso is enough to kill/wound/draw blood regardless.

Dual-wielding snakes.

A pillow. I’m probably going to lose anyway and now he can’t really tell the story of how he defeated a guy armed with a pillow without looking like an asshole.

And, even if you lose, all you’ll be is another day older and deeper in debt.

Bombs connected to computers running the NY Times Sunday crossword app at one kilometer.

First to finish sets off the bomb next to the other person.

Probably nunchucks. They are pretty hard to use, and since I have a little experience with them, that’s probably far more than my opponent.

I’d take a leaf from the book of duelling according to Melfant and Lenfant (1843) and go with billiard balls @ 20 paces.

30 lb dead fish. Pike, lake trout, catfish maybe. Just because it would be amusing to have two people beating each other with fish.

A fresh trout or Point-of-View-Gun would be my first and second choices, but both are ruled out by the OP. Too bad, I could do a lot of damage to an opponent with the gun.
Therefore, I will select the flame thrower. The challenger can decide if he wants to be a little singed or die horribly in a greasy fireball. [reviewed rules] Damn.

OK then, blow gun.

First choice – flintlock pistols, second choice swords. I practice and train with both, something few people do although in this hypothetical universe that could be YMMV. Third choice, just in a pyrrhic sense, would be shotguns loaded with buck. Set the conditions you want, one of us is almost certainly dead.

Machetes. The space is too small for rapiers, I have about a 50/50 shot of getting off first, and fully accept that victory in a knife fight means you made it to the ER.

Well, I was going to say shotguns on ostrich back, but you said no animals. I’d certainly choose a fire arm, though, since even though I took a lot of martial arts in the past, including weapons training for the higher belts, I know enough to know I couldn’t defeat anyone who really knew what they were doing, while pistols or other firearms are something anyone with even a little familiarity can use effectively…and I have more than a passing familiarity. So, pistols at 40 feet I think, maybe a matched pair of .40 caliber Beretta with 10 shot magazines, since that’s the gun I’m most familiar with.

A specific pair of pistols that I have previously modified so that only I know how to actually fire them.

You only have 20 feet. Good thing the other guy won’t have a knife.