I've spent awhile looking around and have yet to see a entirely complete Civ glitch guide, so I just thought I'd make my own so that never again will someone have to ask a question like, "Wait what? Soldier can go Civ?!"
This guide is my attempt at explaining every known and confirmed working (Fastest) Civ methods and all the smaller details about them so that others wont have to wonder why the glitch isnt working for them.
I reccomend you read the universal method first because it works on most servers, and it gives you the basic rundown of how most Civ glitches work if you are new to Civ glitches.

If you have any issues, suggestions, or easier methods I missed dont hesistate to comment.

If a method works on every class it wont be listed in each class' section of the guide. Universal methods only are listed in the universal methods section, And methods that work on multiple classes but not all will be listed in only the sections for the classes they work on.

The Dispenser Method (2 Players - Same Team):
This method only requires one person who wants to perform the glitch and an Engineer on their team to help them achieve it, I find this method is most helpful on maps like cp_steel because of the safe zone in spawn where you can place a dispenser to perform the glitch.
Here's How -
Step 1 : Have your friend on your team place a dispenser down. (It's easier if it's against a wall)
Step 2 : Stand in their dispenser and suicide (type 'kill' in the developer console or use a killbind) while holding any item
Step 3 : Change the item in the slot that you used for the glitch to any other item (ex: if you used the Big Earner, Just switch to Stock)
Step 4 : Stand inside the dispenser once you respawn (if the dispenser isn't pushing you out then it won't work, some servers have team collision turned off, If this is the case then you can't use this method)
Step 5 : While still in the dispenser's hitbox, Try to pick up the item on the ground while holding out the slot that the item will go in (ex: if you are doing the glitch using melee, Just hold your melee out)
When you pick it up, Your hand should refresh and your viewmodel will break (It will freeze in the position it was left in last before you executed the glitch)
Crucial Note: Don't crouch when trying to pick up the item, you have to stand, If you are able to pick the item up while crouching then you aren't far enough into the hitbox for it to work, You have to pick up the item by peeking over the top of the dispenser.
Note: Don't press any item buttons, If you change weapons you lose the glitch (Unless you do the glitch on all of your inventory slots).
Short warning, Performing this glitch actually deletes that item slot, So until you die you are unable to use that item slot, That also means that this glitch makes it possible to literally have no item slots. (There might be some abusable underlying exploits that take advantage of this bug)

Consumable Method (Solo):
This method requires any secondary slot consumable, Such as: Bonk! Atomic Punch, Crit-a-Cola, The Flying Guillotine, or Mad Milk And a killbind
Here's How -
Step 1 : Hold any of the consumable items listed and suicide
Step 2 : Once you respawn use the consumable item but dont let go of the primary attack button (If you use Bonk! Atomic Punch you have to wait for the effects to expire before proceeding to the next step)
Step 3 : While still holding the attack button pick up the item on the ground

Beggar's Bazooka Method (Solo):
This method requires the Beggar's Bazooka and a quickly accessiable taunt bind (or just being fast)
Here's How -
Step 1 : Empty the ammo on your Beggar's Bazooka to 1 in reserve
Step 2 : Step OUTSIDE of spawn (if you pick up an item in the resupply room it doesn't drop your current item on the ground, It just consumes the one on the ground) and suicide.
Step 3 : Once you respawn go outside of spawn and pick up the the Beggar's Bazooka on the floor
Step 4 : Load the last rocket into your clip and, And as soon as it shows up on your hud that the rocket entered the clip
Step 5 : Taunt while the rocket is still in your clip
Step 6 : (Now you should be holding a Beggar's Bazooka with 0 ammo if you did it right,) Now pick up the Beggar's Bazooka on the ground (While still holding the attack button). Now you should have a invisible Beggar's Bazooka in your hands

Airblast Method (Solo):
This method works with any flamethrower that can airblast (Sorry Phlogistinator)
Here's How -
Step 1 : Hold the secondary attack until you only have one airblast left
Step 3 : Go outside spawn and suicide
Step 4 : Go outside spawn and pick up the flamethrower on the ground
Step 5 : Hold the secondary attack button
Step 6 : Pick up the flamethrower on the ground while still holding secondary fire
Alternatively if you are on a server with instant respawn then you can do this method:
Step 1 : Suicide with the flamethrower out
Step 2 : Hold the secondary attack
Step 3 : Once your ammo hits 0, Keep holding secondary attack and pick up the flamethrower on the ground before it despawns

DemoSoldier Method (Solo):
This method is one of the more item demanding ones, But if you already have the items then this one is the quickest to perform ingame because it doesn't involve any respawning, Just refreshing your loadout.
To perform this method you need a shield (Any), The B.A.S.E. Jumper, The Sticky Jumper, And a melee (Any)
Here's How -
Step 1 : Make a Demoman loadout, Equip The B.A.S.E. Jumper, Sticky Jumper, And Any Melee
Step 2 : Make another Demoman loadout, Equip The B.A.S.E. Jumper, Any Shield, And the same melee as the previous loadout.
Step 3 : Equip the first loadout, Hold The Sticky Jumper, The change to the second preset using the developer console (A = load_itempreset 0, B = load_itempreset 1, C = load_itempreset 2, D = load_itempreset 3)
ex: I make the first class in Slot A and the second in Slot B, I Equip Slot A and hold the Sticky Jumper, Then open the console and type 'load_itempreset 1', Now I'm holding a invisible Sticky Jumper.

Minigun Method (Solo):
This method only requires a killbind and ANY minigun (The Huo-Long Heater is the fastest, But any of them work.)
Here's How -
Step 1 : Hold the primary attack button to both rev and fire the minigun
Step 2 : Get the ammo as close to 1 as you can
Step 3 : Go outside spawn and suicide
Step 4 : Go outside spawn and pick up the minigun on the ground
Step 5 : Hold the primary attack button
Step 6 : Pick up the minigun on the ground while still holding primary fire
Alternatively if you are on a server with instant respawn then you can do this method:
Step 1 : Suicide with the minigun out
Step 2 : Hold the primary attack button to both rev and fire the minigun
Step 3 : Once your ammo hits 0, Keep holding primary attack and pick up the minigun on the ground before it despawns.

Lunchbox Method (Solo):
This method requires The Second Banana, The Sandvich, Or The Dalokohs Bar (Preffered) (The Buffalo Steak Sandvich won't work because it automatically switches you to melee afterwards)
Here's How -
Step 1 : Hold your Lunchbox item of choice and suicide
Step 1.5 : (If you aren't using The Dalokohs Bar): Take Damage (The Sandvich and The Second Banana don't get consumed if your health is already full)
Step 2 : Eat your Lunchbox item but don't let go of the attack button (Now you should still be holding your Sandvich even though the bar isn't full)
Step 3 : Pick up the lunchbox item on the ground

No known Solo method for Engineer yet, Refer to the universal method for this class.

No known Solo method for Medic yet, Refer to the universal method for this class.

Jarate Method (Solo):
This method requires the Jarate secondary
Here's How -
Step 1 : Hold the Jarate and suicide
Step 2 : Once you respawn use the Jarate but dont let go of the primary attack button (If you use Bonk! Atomic Punch you have to wait for the effects to expire before proceeding to the next step)
Step 3 : While still holding the attack button pick up the item on the ground

No known Solo method for Spy yet, Refer to the universal method for this class.