A Sneaky Dickens attack is when someone gets up from from their seat at a bar or restaurant and leaves their coat temporarily unattended. The attacker quickly draws a penis on a napkin or scrap of paper and puts it in the unsuspecting victims coat pocket for them to find at a later time. Some more advanced attackers may even have penises drawn on many pieces of paperahead of time so that they can carry out attacks more efficiently and with less risk of being caught since their "ammo" is pre-made.
"When I got home from the bar last night my coat pockets had a bunch of dick drawings in them. Someone gave me a Sneaky Dickens."
The term originated from Shakespeare's play "The Merry Wives of Windsor," in the 16th century. It is a term used in polite society to mean the Devil! (It has nothing to do with Charles Dickens.) The word appeared in a sentence (although sounding odd in modern day language) "I cannot tell what the dickens his name is my husband had him of."