A word, many ways to use it.

Some variations are locked into specific phrasings and or contexts. For example, "shithead" and "shit-for-brains" can only be used to refer to a person or persons; the former asserts that the person is irritating, the latter that s/he is stupid. If something is "a shit", then it is annoying or dysfunctional, but if something is "a piece of shit", then it is of extremely low quality. If you "give someone shit", you could be giving them something worthless, but it is more likely to mean you are insulting them, often with the implication that you are trying to provoke a response. To "sling shit" is to hurl insults or aspersions, and a "shitslinger" is a person, especially a politician, who makes a habit of doing so. The ubiquitous "shit happens" is a self-sufficient statement of resignation to ill fortune. These sorts of restrictions can be subtly different from one locale to another, and are subject to very rapid change.

-He's just talking shit.

-That poem has got to be the shittiest thing I've ever written.

-Do you really think my hair looks good, or were you just giving me shit?

-The pasta was okay, but the coffee was shithouse.

-That piece of shit hasn't worked properly for years.

-Give me a break, I've had a really shitty day.

-He's been a grumpy little shit lately.

-I wonder if anybody makes shittier burgers than McDonalds?

-Nah, relax buddy, I was just shitting you.

-That newspaper article was total sensationalist shit.

-Does he really think we're going to believe his shit?

-We've got to get it finished in the next hour, I shit you not!

-Quit fooling around with that shit.

-You'd better not mess your shit up with my shit.

-Shit! That shit is some bad shit.

-You wouldn't be bullshitting me by any chance would you?

-Well, the fire alarm went off and then everybody just kinda went apeshit.

-This lamer was too chickenshit to go bungee jumping with me on the weekend.

-After I hit the pub on Friday night, I was so ratshit I couldn't make it up the stairs!

-No more stupid examples.