A person that is so worthless you would contemplate hanging out with a sack full of doo doo rather than be around them. A person that constantly needs to be reminded that they are worthless because they do not realize it.
Damn- i need to get outta this party, all I see are dumpsacks.
We had to cut that kid from our team, he was such a dumpsack.
A sack of weed that is both skimpy and poor quality...and smashed. Derranged from the term "skimpsack".
An example of a dumpsack would be weed you buy from some cracked out wierdo who calls the weed "dense", but is just smashed from them sitting on it.