Your coworker came to work looking really scruffy. His hair is messed up, his clothes are wrinkled, etc. He doesn't usually look this way, so you're worried about him. When someone comments on how he looks, you say this.
One of your coworkers came to work today with a dirty shirt. His hair is also uncombed and he has a little bit of stubble. You're talking with a coworker about him. You say this.
Your friend has a hangnail. She complains about it. You want to offer to help her, so you say this.
You've been having lunch with a friend and just noticed that the skin around your fingernail hurts. This is what you say.
You've just finished giving a 15-minute presentation at an event for people to practice giving speeches in English. Now you want to give the audience a chance to ask you questions, so you say this.