Sineap is the term "paenis" backwards. Usually useful in writing codes, "sineap" can be written in most public spaces without being recognized by authority figures. The "A" is added into the term "paenis" to add a comical twist; The "A" causes the word to sound like it is being said by a someone from the south, thus causing whoever says the word to sound stupid. (Inventors of the word sineap are not implying all southerners are stupid) Sineap is most commonly used in anger.
SINEAP!!!!!!! I JUST STUBBED MY TOE!!!!
YOU'RE A GIANT SINEAP!