5. Nf6?? was the decisive blunder. After that move black was lost.
Chasing a Knight

I honestly think 3...Nd4 was the blunder. other than the trap, that move holds no value. Black would have been better off playing 3...Nf6 and developing his pieces instead of trying to trick the opponent into falling into a trap.

I'm not sure if Nf6 was a blunder. I played this position just now with a computer and after e5 he should have played d5! pretty much equalizing. A lot of times d5 is a good response to e5. I agree that Nd4 is a bad move other than the trap.
Sorry, I'm not good, but I don't see how 4. Nxe5 leads to the loss of Knight. I only see it leading to the loss of a pawn and black having a highly undeveloped position.

Sorry, I'm not good, but I don't see how 4. Nxe5 leads to the loss of Knight. I only see it leading to the loss of a pawn and black having a highly undeveloped position.
here's the trap.

Yep, that's the trap. There's not much else white can do after Qg5. I found an interesting article on 3...Nd4. http://www.chesscafe.com/text/mcgrew25.pdf
I was actually thinking of 5. Ng4 to block the Queen attacking the pawn. 5... h5 to force the Knight to move 6. Ne3 would still protect that pawn for the time being. I'm not good enough to plan out many moves after that, though.
I'm new to the site but I was happy about this game against a higher rated player. He deserves it for that tricky Nd4!