Challenging an adjective with "shenme"
Adding 什么(shénme) to the end of an adjective can be used to form a rhetorical question. In the phrase 你担心什么, "what are you worried about?", the speaker is implying that there is no need to be worried.
Some examples:
- 你紧张什么,你不是上过好几次的舞台吗?应该早就习惯了吧。
- 你郁闷什么,看这蓝色的天空,绿油油的田园,我感到生活太美好了!
- 你急什么急, 还早着呢。
Like in English, "what are you worried about" can be a rhetorical question, and can also be actually inquiring about what exactly the listener is worried about. The same is true in Chinese, so context and tone of voice is important in understanding what the speaker means.
If the adjective is a single character, it can be repeated after 什么, as in the last example sentence, which can be used to give further emphasis. It almost has a tone of incredulity, a bit like "what on earth are you worried/anxious about".