没图你说个贾斯汀比伯
Méi tú nǐ shuō gè jiǎsītīng bǐ bó
A direct translation of the phrase is "If you don't have a picture, you are just talking a Justin Bieber", which does not really make sense. Instead, People usually say this when they require to see a picture of what you just described.
贾斯汀比伯 is actually Justine Bieber in Chinese. By why Justin Bieber?
The acronym of Justin Bieber is JB, which means penis in Chinese. Penis can mean a lot in Chinese, but in this particular context, it basically means “nothing”.
An example of how you use this phrase:
A: 刚看见一个人长得好像贾斯汀比伯！
I just saw someone and he looked a lot like Justin Bieber!
B: 没图你说个贾斯汀比伯。
If you don't have a picture, you ain't sayin' nothing
[People make fun of Justin Bieber a lot in China.]