An exclamation or ejaculation expressing disquiet, disgust or disappointment with a given situation. "Rats arses" is an acceptable substitute for more polite occasions.
As in "Rats' cocks! That was my last fag."
Or simply "Rats' cocks!" when, for example, treading in a dog shite.
Ralph: So this morning, I was in such a rush that I grabbed any two socks I could find and put them on. To my dismay, I noticed that my left foot was covered in something wet...turns out I had accidentally grabbed my Ratsock.