"靠谱(kào pǔ)" is a slang term commonly used on a daily basis by Chinese people. It literally means "to be reliable" or "to be worthy of trust" and is used to refer to a person or something that one believes to be trustworthy. Conversely, "不靠谱(bú kào pǔ)" means the opposite. When Xiao Li complains to Simon that his new colleague Lulu is an unreliable person, Lulu suddenly appears. 

        
         zuó tiān wǎn shàng wǒ děng nǐ dào shí diǎn
Xiao Li: 昨天晚上我等你到10点。
         Last night, I waited for you until 10 pm.

      duì bú qǐ wǒ bú shì gù yì fàng nǐ gē zǐ de
Lulu: 对不起，我不是故意放你鸽子的。
      Sorry, I didn't mean to stand you up.

         tài bú kào pǔ le wǒ yào hé nǐ jué jiāo
Xiao Li: 太不靠谱了，我要和你绝交！
         You are totally unreliable. Our relations end here!

      dé le bié xiǎo tí dà zuò le
Lulu: 得了，别小题大做了。
      Come on, it is not a big deal.

In the dialogue, Xiao Li is furious with his friend Lulu for being kept waiting for such a long time the previous night. Lulu apologizes and says she didn’t mean to "放鸽子(fàng gē zǐ)", which literally means "fly a pigeon". This phrase is used when someone is a no-show for a meeting, much like the term ‘being stood up’ in English. We can say,"我被放鸽子了" (I’ve been stood up), or "她放我鸽子了" (She stood me up).

"靠谱(kào pǔ)" is an adjective to describe a person or a thing. If you trust a person, you can say,"他是个靠谱的人" (He is a reliable person). If you think a task can be finished with a very high success rate, you can say "这个方案非常靠谱" (This plan is very reliable). In the dialogue the opposite word "不靠谱" is used to describe a person as being unreliable because they did not show up for a pre-arranged meeting.  

The idiom "小题大做" (Literal meaning of each character: small-problem-big-do) is basically the same as the English idiom "making a mountain out of a molehill". The idiom is used to describe when someone overreacts to a trifling problem.