Most of Chinese are modest.For example,if you say“you are beautiful”,we will answer“一般一般” .It is just a kind of manner in China.But tis sentence is interesting,when you praise someone,to say they are awesome.Because of the habit and the modest of Chinese,they will say“一般一般”.But he think he is awesome,too.He will say“I am just the third in the world.(世界第三)”.It is a kind of humous.But it is only a joke.You would better say it with your friends.

哈哈，that's means : " i'm not very great,i'm very so so , just the third of the world (the bronze on sports)" actually it's a contrary mean. it's seemingly modesty ,actually it's very pride. usually people say it as a joke do you understand?

It's just a kind of quip. People who say this is pretending to be modesty. "一般一般" means "just so so", but they think that they are "世界第三 (the world's third)". And "一般一般" and “世界第三” are in rhyme. Don't need to take this seriouly, it's just a joke.

Sort of like saying, "Oh, I am not so great really. I am only the third greatest in the world." Dui ba?

Ha,it's a joke! It just like someone says you're so good at something and you answer in a humor way. eg.'Wow,how did you do that?You're such a genius!'' and you say:''一般一般，世界第三。''