How do I best defend against the king's gambit as black?

Of all the chess openings I hate the most, it is the king's gambit. I haven't played against it too much and it always makes me pause in my tracks. Here's my latest game against the KG. What should I have played? Should I accept the KG or decline? 

Always accept, but then give the pawn back for the sake of good development.

Early d5s are common and popular even at GM level, so that's worth looking into.

I like 2...Bc5

Neither of these treatments aim to refute it. It just gets black a "normal" position.

I just play g5 Bg2 h6 and don't let they take the pawn back if they don't play h4. Those pawn can be used to attack after they castle

Bobby Fischer lost as Black against Spassky.  Then he wrote an article refuting the KG by accepting the pawn.

"The main advantage of the King's Gambit is there are so many refutations that black can't play them all at once and he's got this problem he has to decide which one to go for and then he loses on time." - Nigel Short. 

OP played the "Fischer defense" in the OP... I guess you didn't recognize it.

5...h6 - Fischer

Unsurprisingly the OP didn't know the theory after 3...d6

I used to play it, but stopped after my opponent knew move 15 and I only knew up to move 14. Too much effort to do upkeep when you see the opening so rarely. Sane people who aren't pros shouldn't play theory heavy lines of the KG as black... IMO.

play this and suck the life out of the position

establish your kingside pawn chain, retain your extra pawn, and clamp down on white's position

There's some game between Magnus Carlsen and Ding Liren where Ding Liren destroyed the King's gambit with this, I forgot when it was though

There's a bit of a nasty trap in the classical variation for black if white doesn't know what they're doing. You should never just play an opening just for the trap though (Learn of the some theory behind it)

Anyone who plays the King's Gambit regularly knows not to do that

I must have misunderstood the Fischer Defense! Thought I played the Fischer variation myself, but doesn't go like that.  Of course I imagine of the two of us, you are correct! But I always thought this was it:

That is how I always try to play against the K.G. and seems to do pretty well! But at my level the opening doesn't decide games. 

3...d6 is the variation Fischer proposed after his loss to Spassky... the OP didn't play it as well as Fischer, but I don't really think that matters

@llama47 Ahh ok fair enough lol.   It simply becomes the Fischer variation a couple moves sooner than I thought.  Was thinking you had to play h6 & g5  too.  Thanks! 

@Optimissed  g5 is bad stuff?? Ut oh, better re-think my approach Lol.  Interesting though, hadn't heard of a Victorian variation. 

I think this variation gives Black a nice practical advantage:

About 1985 or so, I followed Fischer's advice in his little pamphlet in a USCF postal chess game and got creamed. I don't trust his analysis. Too short and glib to be of much use.

There was a saying at the OTB club where I played casual games. Something like "but he's Fischer and you're not." It may have been an old quote but I don't know.

Essentially any time someone tried to excuse a move by "I know it looks crazy, but I saw [insert GM name here] play this move, the response was "but he's _____ and you're not."

In other words, it might be a good move, but you obviously don't understand why it's a good move, so it's the same as playing a bad move

You might want to look at the Falkbeer Counter Gambit: 2...d5. After 3. exd5, Black has several interesting continuations.