The expression "你懂的 (nǐ dǒng de)" was translated from the English expression "you know." Its popularization is due to a video Old Boy, made by the Chopsticks Brothers. It's a story about two middle-aged friends who combine their talents they learned in middle school to participate in a sort of "China's Got Talent" competition. In the video, the expression "你懂的 (nǐ dǒng de)" expresses an acknowledgment of their shared nostalgia of youth. Ever since then, "你懂的 (nǐ dǒng de)" has become a popular expression when two people share a mutual comprehension of a time or feeling. The phrase simply means, "you really do understand," mixed with the French mood of "c'est la vie!"
Nowadays, the saying is frequently used to assure an understanding between two people in conversation. Next time you find yourself in a situation where details aren't convenient to say out loud, a simple "你懂的 (nǐ dǒng de)" conveys "you understand what I'm talking about."
Mike, nǐ zěnme hé Mary zài yì qǐ le?
Mike, how come you are now with Mary?
Xiǎo diǎnr shēng, nǐ dǒng de…
Keep it down, you know what's been going on…
Zěnme le? Chóuméikǔliǎn de.
What's wrong? Why such a long face?
Wǒ wàngjì zhǔnbèi lǎobǎn yào de wénjiàn le, jiéguǒ… … nǐ dǒng de.
I forgot to prepare the documents for my boss, so now…well, you know what'll happend.