Alright, I've got a couple. All names are placeholders; it's the stats that count.
Made sure every weapon here is theoretically possible using the optf2 link provided.
Going with Sniper and Pyro primaries for today.


Primary:

The Laughin' Stock (Stock Rifle Variant):

• On headshot: deals 25% explosive damage and knockback to nearby enemies.
  
• +100% explosion radius.
  
• Critical hit forces victim to laugh. (stun)
  
• Critical hits do no damage.
  
• No headshots when not fully charged.
  
• No random critical hits.

The Outback Outbreak (Stock Rifle Variant):

• +200% bullets per shot. (3 bullet spray)
  
• Charge and fire shots independently of zoom.
  
• Additional knockback on target and shooter. (similar to Force-a-Nature)
  
• +25% charge rate.
  
• Fires tracer rounds.
  
• 15% less accurate.
  
• -50% damage penalty.
  
• No headshots.

The Flarrow (Huntsman Variant):

• Inflicts afterburn.
  
• Projectile knocks back target on hit, and explodes when it hits the ground. Increased knockback on burning players. (Scorch shot on-hit effect, allows single projectile to connect w/ target twice.)
  
• Mini-crits burning targets.
  
• Projectile cannot be ignited by friendly pyros (already deals afterburn)
  
• -25% damage penalty.
  
• No headshots.

Primary:

Cowblaster or something. (Stock Flamethrower Variant):

• Alt-Fire: A charged shot that mini-crits players, sets them on fire, and disables buildings for 4 sec (Fires a charged Cow Mangler Rocket on alt-fire)
  
• +150% ammo cost on alt-fire
  
• No airblasts

Uh... Mmph? (Stock Flamethrower Variant):

• Reflected projectiles deal full critical hits where they would normally mini-crit.
  
• +150% ammo cost on alt-fire
  
• No random crits