1. Skjerp deg
This phrase does not bode well for you. It usually means you’re making an idiot of yourself. “Skjerp deg” could be translated as “Sharpen yourself up,” and it’s used in all sorts of contexts.
Teachers use it to tell students to pay attention. I yell it at friends who are doing something ridiculous. Cops use it to tell off criminals who are obviously lying to them, parents say it when telling off their five-year old who has just drawn with crayons all over the new wallpaper.