Skin is not only large, but it is important. One of its jobs is to protect us, keeps bad things out. But sometimes it fails. (extreme) small bugs, called mites, can get under our skin. And when they do, they cause itching and great discomfort. So, to get under someone's skin means to annoy them or to bug them. That's just one definition of the (express) "to get under someone's skin." It can also mean that someone is very (attract) to you. You can't stop thinking about them. You might even be obsessing （着迷）about them.
There are many ways (describe) people using the word "skin." If someone is thick-skinned they are not easily hurt emotionally. You can criticize them or be unkind to them and it simply rolls off their back. Thin-skinned people, , are easily hurt by criticism, even if it is not too severe. You have to be careful about you say to thin-skinned people so as not to hurt their feelings.
If someone is suddenly very (scare), you can say they nearly jumped out of their skin! For example, one day I saw my friend Sierra (wait) at a bus stop. She was wearing headphones and did not hear me come up behind her. So, when I (touch) her shoulder, she nearly jumped out of her skin!
