A particularly unattractive ex girlfriend or boyfriend who insists on hanging around you and making themselves the center of your attention. The etymological root word is "Cynosure", an object at the focal point of attention.
"I wish she'd just leave me alone, but she's like a Cynosaurus Ex or something"
When you fail at something in life (eg. failing an exam or not getting a job), go home and spend an hour just standing in the shower, propping yourself up against the wall with your eyes on your feet.
Caleb knew the only thing to do after he didnt get prefect was take a failure shower.