Khloe Kardashian is going through hell right now but trying to put on brave face to the world ... or so it seems. 

Khloe tweeted a picture of herself Friday night -- looking flawless -- and NOT looking like a woman on the brink. An hour later she offered an explanation, writing "Smile and no one will notice."  A pretty clear message.

TMZ broke the story ... Khloe is trying everything she can to save husband Lamar Odom from his downward spiral, which stems from an intense crack addiction.