How did I lose?

This guy had the lamest opening I've ever seen... and he was wandering around the board with no plan... then he totally destroyed my kingside and I lost the game. What happened?

It goes to show the lack of importance the openings are for lower rated players. However, you're wrong that your opponent didn't have a plan. The pawn storm on the kingside started fairly early.

It seems the main problem began with your choice of 12. Nd3. Things might've turned out differently with 12. Nxg4. Nd3 blocked the defense of the d4 pawn. Though i have a feeling you'd still lose. IMHO your opponent seems better than what the opening would lead a person to believe.

Could have castled queenside

d4 & e4 is difficult to play.  It controls the center.... but now you have to play sharp to avoid losing those pawns or facing overworked defenders to maintain your presence in the center.

12 Nxg4 is one thing that seems like it would have helped greatly.

13) central pawn needs defense.  From here on his bishop becomes a 9 point value piece due to its position, you really, really, really needed to trade it or force it to move or block it.  (Self pinning the knight isn't blocking it, that allows all sorts of mischief later).

21) I think you have to play rook takes bishop here.  The pawn move is of no lasting value and may even have helped his attack.

Actually, it seems your opponent might have had you beat even earlier. Psychologically, he had the advantage of you underestimating his play.

I've seen mention of move 12, but no one has really mentioned move 9.  It looks to me like castling here was your first major error.  The pawn storm is coming on the king side and you castled right into it.  White had also already weakened the king side pawn structure, giving black a target. 

Also, black's g pawn is hanging here.  It is a little dangerous to take (9.Kxg5) because it gives his knight a potential discovery, but atm this discovery is not a threat (the knight can't safely move to an active square, though he could force a trade, you're still up at least a pawn).  And if after 9.Kxg5 h6, your bishop can retreat to h7 or advance (my preference) to e5 putting pressure on that knight.

8. A mistake because bd6 is better.

9. A mistake because I castled into his pawn storm. Should've waited and castled queenside.

12. A mistake because I blocked my queen's defense of my pawn. Should've played nxg4.

13. A mistake because I didn't defend my d pawn.

21. Should've traded my rook for his bishop.

Thanks guys.