Something that is not expectable.

Definition: unexpected and inexcusable
Root: Middle daughter in heated discussion with older daughter over pool ettiquette

Like a surprise party but instead of balloons and cake, there's suicide bombers and explosions. Usually beginning with the phrase "ALLAHU AKHBAR"

When a person with a penis, in a sneaky manor, gets on on all fours like a dog, and tucks their penis and tesiticles between their legs. They then simultaneously shake their phallic-tail and howl at the moon, surprising an unexpecting bystander.

Interlocking your two hands in the "Shocker" position, then inserting them into a woman.

Expect that what is not predicted will happen.

They come along after a very satisfying and presumably finished bowel movement, post cleanup.

Me: "I just had an unexpected guest."
Me : "We're out of toilet paper."

Her: ~closes eyes, shakes head~

poop
feces
turd
shit
crap
bowel movement