Challenging a verb with "shenme"
Adding 什么 (shénme) to the end of a verb can be used to change a sentence into a rhetorical question.
Verb + 什么 + Verb
Just like in English, asking "what are you looking at?" can be a rhetorical question (hinting that you should stop staring), but can also be a sincere inquiry about what exactly the other person is looking at. When you repeat the verb, though, you make it pretty clear that you're not just curious. You're so annoyed that you're asking a rhetorical question.
Verb + 什么 + Verb ？
- 你 买 什么 买，钱 都 花 光 了。Buy what, now? We spent all of our money.
- 你 哭 什么 哭，又 不 是 没有 你 的 礼物。What are you crying for? It's not like there's no gift for you.
- 你 笑 什么 笑，看 我 做错 了，你 很 开心 吗？What are you laughing at? Does seeing me make mistakes make you happy?
- 你 说 什么 说，大家 都 不 说话 ，就 你 说话 。Why are you talking? Everyone else isn't saying a word, it's just you talking.
- 你 看 什么 看，没 见 过 美女 啊？What are you looking at? Haven't you seen a pretty girl before?
Verb + 什么 + Object
This pattern is often used with separable verbs.
Verb + 什么 + Obj.
This usage is best illustrated with examples:
- 离 什么 婚 ！你们 结婚 才 三 个 月 。What are you talking about, "divorce"?! You've only been married three months!
- 道 什么 歉 啊 ，又 不 是 你 的 错 。No aplogies! You didn't do anything wrong.
- 开 什么 玩笑 啊 ，你 撞 了 我 ，我 还要 跟 你 说 “对不起” ？Is this some kind of joke? You ran into me, and now you want me to say sorry to you?
- 没有 钱 看 什么 电影 。What movie can we go see when we're broke?
- 还 吃 什么 早饭 啊 ，要 迟到 了 。No time for breakfast. We're going to be late!
Note that the questions above would likely be between friends, or at least two people who are quite familiar with each other. Tone of voice and context is key.