cocô do cavalo do bandido

Etymology
lit. 'the crap from the bad guy's horse'.

Noun

 * 1)  a person or a thing that is extremely worthless

Usage notes
Often extended with random words with increasingly inferior status for emphasis, as in possibly "a sujeira da pata da mosca do cocô do cavalo do bandido" (the dirt in the paw of the fly of the crap from the bad guy's horse).