If something is "Murks" then it´s simply shit. usually the product of someone´s inability to do just the thing he/she/them tried to do. Can also be used for describing something: he totally murksed it.
Person1: Look at that picture th artist sold for 4000.
Person2: What the fuck?! That´s total MURKS! A drugged ape would do much better!
Person1: Heard of Bill proposing to Jane?
Person2: Yeah he toally murksed it. I can till see how swollen his left cheek is.