The mimic polymorphs into a semi-truck

I feed the mimic 5323 peas

The mimic spits out 10646 green beans.

I feed the mimic my character sheet.

The mimic then begins to chew at you until it has consumed you whole. Then you find yourself in an empty field as your character(the one you fed it).

I feed the mimic a black top hat.

 He spits out a pair of sandals, with razor blades attached. I feed him the most annoying party member.

he spits out a balor and 10 pit fiends that try to kill you

I feed the mimic AnonymousUser777

The mimic spits out AnonymousMouse666.

I feed the mimic the Reddit servers

he spits out DDB servers

I feed the mimic 1217583 PP

The mimic spits out 1216849 bronze coins from an ancient civilisation.

I feed the mimic a chest (smaller than it) containing 435 pairs of slippers.

it spits out a chest containing 870 pairs of slippers

i feed the mimic the can we get a super yatzee thread

it spits out a Player's Handbook.

i feed the mimic an old cat.

it spits out a kitten

I feed the mimic this tread

a mimic eating a tread grows wheels

I feed the mimic this thread

It spits out the Super Yahtzee thread.

I feed it a Super Yahtzee

it spits out a die that only lands on 20 when you roll it but 1 for everybody else

I feed it the twist the wish thread

The Mimic gives you exactly what you want, no strings attached. (what a twist)

I feed the mimic a red dragon egg

The mimic spits out a very confused dragonborn paladin he says he came from the land of Water?

I feed the mimic the razor blades of my sandals (earlier post)

The mimic spots out a sword.

I feed the mimic its own tail.

It howls in rage-filled pain, and dies.  HOWEVER, behind it is a slightly larger mimic shaped like a door, which spits out an exact clone of the original mimic.

I feed the mimic this meme:

It seems entertained, and spits out a laughing Duergar. 

I feed it a Gnoll.

It says in a deep voice, "Regular Gnoll! Regular Gnoll!" and spits out a badge that says, 'I watch Critical Role'.

Turns out that the mimic is a human Critter who crossed the wrong wizard and is now a mimic. The mimic's name..?

JOHN CENA!!!!

I feed it a druid wildshaped into a tiger.