Can't be depressed
This is a depression meme, and also a roll safe meme This is actually a pretty sad meme - I am not sure if it qualifies as dark humor, but it is pretty bad if you think about it. That being said, the humor in this meme is based on the absurdity of his statement. What he probably means is "You can't recognize if you are depressed if you have never been happy", but perhaps what he means is "your emotional state cannot be lower than usual if you have never had it higher than usual". The implication is that he intends to avoid happiness so that he will never be depressed.
Combine that idea with the look on his face, and the whole is very dissonant. That dissonance is also humorous.