Payday loans come to mind - they definitely aren't illegal, have tons of predatory practices built in, but are universally (at least in my experience) seen as a scam.
I've been told by several people that used to work at large payday loans company: "Under no circumstance should you or anyone you care about get a payday loan. Go beg for money, steal food, whatever you need to do to survive, but never get a payday loan".