The disappearing salami is another term for banging your mom. This term is disguised as a "Magic Trick". This word is told to naive people or small children what you were doing in there mother's room.
Kid- What were you doing in my mom's room?
Strange Man- I was preforming a magic trick!
Kid- What's it called?
Strange Man- Shh its a secret...
Kid- Tell me!
Strange Man- The disappearing salami...
Mom- Arthur, come back to bed!