a bad penny always turns up

• a bad penny always comes back
• the bad penny always comes back
• the bad penny always turns up

a bad penny always turns up

1. A person or thing which is unpleasant, dishonorable, or unwanted tends to appear (or reappear), especially at inopportune times.
   • 1952, Ralph Morris Goldman, “The Money-Changers at the Ballot Box: A Study of Republican Election Buying,”, in The Future Catches Up, Vol. 2, published 2002, →ISBN, page 89:

     It has been wisely said: “A bad penny always turns up again.” . . . Merwin K. Hart turns up again and again. And the Money-Changers of the Republican Party have knowingly sought to profit from Hart's lobby activities.

   • 1989, Jeffrey Boam (author of screenplay), Indiana Jones and the Last Crusade, (excerpts at wikiquote):

     Elsa Schneider: I never expected to see you again.

     Indiana Jones: I'm like a bad penny. I always turn up.

   • 2005, Ron Greer and Mike Wicks, Fire from the Sky: A diary over Japan (2013 iUniverse edition), →ISBN, p. 184 (Google preview):

     Being superstitious was common among a lot of the military. . . . Aircraft were given names such as The Bad Penny (as in a bad penny always turns up).

   • 2011, Gail Bowen, The Further Investigations of Joanne Kilbourn‎, →ISBN:

     I had managed to avoid Julie for almost four years, but, as my grandmother used to say, the bad penny always turns up, and Julie Evanson was one very bad penny.

2. Things that are done improperly eventually cause problems.

• Sometimes used in a jocular or self-deprecating manner, as in:

• 2013 Jan. 20, Ranger Bob, "The Retread Ranger Blog: Where Have I Been?," www.bobmackreth.com/blog (retrieved 25 March 2014):

  But I'll be back—as my mother used to tell me when my dad was late coming home from work, “Don't worry. A bad penny always turns up.”

• bad penny

• “a bad penny always turns up”, in OneLook Dictionary Search.

• Gresham's law in Wikipedia