A fictitious creek, that has shit flowing just like water would normally flow. As a figure of speech, one might say "I am drowning!", but if it worse than that, one may say "I am drowning in shitcreek".
If one creek did exist, one would probably have more of a chance of living after falling in shitcreek, than a normal creek, due to the viscosity of feces being higher. Most people usually do not think about this, because it’s not something you think about.
"If you do not complete that proposal, we are going to be 15 miles up shitcreek."
A pro-wrestler who is so unable to perform basic actions correctly and at the right time, that they almost certainly are unable to wipe their arses properly, leading to them walking around with their arses being all shitty. Hence, shitarse.
Man, I just watched a match involving noted shitarse Magnus. He's fucking terrible, at everything.
"I'll take my turn in the bathroom in a couple minutes right after I smoke a shitarette."
"Want to finish this half-smoked grit? I just needed a quick shitarette and it already did the trick."
"Get out of the bathroom!" yelled Jeff as he shut the front door and removed his jacket, having just returned -- buttcheeks clenched -- from his morning shitarette.