Here are some ideas (although I like 'Dagwood's neighbor Herb' very much).
Scofflaw -- someone who shamelessly ignores his financial and other legal obligations; this only intersects partially with what you're looking for, I think.
Scrounger -- a person who borrows from or lives off others.
Moocher or mooch -- from to mooch, to borrow a small item or amount without intending to return or repay it.
Schnorrer (Yiddish) -- I'm not sure if this matches up well. The definitions I've found on the internet don't seem to, however, the same word in German works great.
(If things get really bad, you could say parasite -- but that is very strong.)