(Shamelessly stolen from an imgur dump, but I felt like it belongs here)
Edit:
Since so many of you suggested additions, I'm just going to list them all in one place. Let's create a community-made enzycrapedia of shit-related terms and phrases!
Transcription of the image in case the picture disappears:
Dogshit: Very poor quality
Bullshit: Not true
Horseshit: Nonsense
Apeshit: rambunctious
Batshit: insane
Chickenshit: coward
Ratshit: poor quality
No shit: obviously (also sometimes "No shit, Sherlock!" as an exclamation)
Holy shit: mind blowing / unbelievable
Hot shit: very good
Dipshit: a total dumbass
Tuff shit: take it or leave it. (correct spelling would be "tough shit")
Jack shit: nothing
The shit: perfection
More shit:
Cut the shit: knock it off.
Are you shitting me: are you serious.
This shit is bananas: this is crazy.
That’s my shit: I really like that.
I dig that shit: I love it
Shit!: An exclamation of discontent. See also: fuck.
I shit myself: I pooped my pants.
Shit-Hawk: unpleasant person
For shits and giggles: Doing something silly for no particular reason
Shit a brick: to be scared
Scared shitless: being really scared
Shitstain: someone trashy or worthless
Shit for brains: stupid
Shit sandwich: a shitty situation
Shithead: a shitty person
Shithole: a shitty place
Piece of shit: a shitty thing
Deep shit: a meaningful revelation
To be up shit creek (without a paddle): to be in deep trouble
To be full of shit: constantly lying
Shit Stirrer: someone who deliberately causes problems/arguments
Get your shit together: to organize stuff properly (alternatively; to calm down)
Losing your shit: freaking out
To [do] the shit out of something: doing something in an excellent way
I don't give a shit: I don't care
When shit hits the fan: when an already bad situation suddenly becomes worse
Shit happens: bad things happen and you can't do anything about it
Shit just got real: Something dangerous is happening right now
Does a bear shit in the woods?: Isn't it obvious?
Eat shit: To fall on your face
Shit-eating grin: a smug and condescending expression
Who shit in your cereal?: Who ruined your day/mood?
(To watch the) Shitshow: watching utter chaos unfold without intervening
A metric shit ton: a lot
Shit on a Shingle: a dish consisting of a cream sauce with meat in it poured over toast
Nuttier than squirrel shit: being crazy
Shitstorm: a stressful, chaotic situation
You don't know shit: you're clueless
Don’t shit where you eat: Don’t date a work colleague
The shits: diarrhea
My shit: my stuff
Shitter: toilet
You are shit: you're worthless
You are not shit: reassuring that you're NOT worthless
You ain't shit: you're worse than worthless
Thanks and credit to: Poopmeister, Wogi, protist, cloudy1999, lambchop and ToRa