Commonly used on internet forums, "shit sucks" is short for "This shit fucking sucks", meaning "This situation is horrible."
I got run over by a car. Shit sucks.
I got the flu the day before graduation. Shit sucks.
My girlfriend dumped me after I bought her an expensive gift. Shit sucks.
I realized that I was wearing only my underwear at the interview. Needless to say, shit sucks.
Used to describe a very unpleasant situation. Past tense would be "shit sucked"
"On my way to work today some jackass slammed into my car and completely smashed my bumper. I have like no money to get it fixed right now. Shit sucks."