The centre-back accepts he will never fully get over the hurt of that occasion after Championship side Cardiff had defied the odds to reach the final.
But Johnson is looking to make a return trip to Wembley - in the first instance in the semi-finals - by helping Blues to topple Avram Grant's side.
He said: "I'd love to get back there. I had a good couple of games there with Cardiff in the cup a couple of years ago.
"It was a disappointing end so I'd love to get back there and put it right.
"We were the underdogs. We had a bit of luck with the draws but everybody who got put in front of us, we beat them.
"You can't be that fortunate to get to a final. We beat the sides we faced and we were there on merit.
"It was special. Being a Championship side, getting to a final, we made a bit of history.
"But it took me a long time to get over the initial disappointment. I drove my wife mad. It took about eight months.
"It bugged me, I kept watching the game and my wife would come in and I'd be sat there watching it and she'd say 'what you doing?"'
Johnson added: "It's one of those things. I couldn't deal with the loss and the disappointment.
"I'll never get over it, I'm not over it now. But the initial disappointment, the sulking and being upset was a long time ago.
"That's how I am, I'll end up with ulcers when I'm old with worry!"
Johnson is new to the top flight after his summer move from Cardiff but is not afraid to voice if his opinion if he feels something has to be addressed.
He said: "I have been like that over the years. I probably still am now but you obviously have to be careful with what you say.
"With the players we've got now, it's difficult to hang people out who have been doing it for years.
"I've just come into the Premier League but I'm not scared to say something. If something needs to be said I'll say it.
"I am one of them guys who will say something if things haven't gone right in the first half.
"We've got a good few who are like that and, if it needs to be said, will get it out in the open.
"If somebody is not doing their job, then you've got to make them aware of it so they'll do it for the second half. Then the gaffer kind of calms you down and has a little pop himself."
Johnson believes Portsmouth have the right to still be in the competition despite having gone into administration.
He said: "Should Portsmouth still be in the cup? I don't know, probably. If they had gone out of business, then it would have been a different story.
"They've taken their punishment, they've been deducted points which has more or less guaranteed relegation now. I think that's enough.
"They'll be looking forward to a cup run now that the league has effectively ended for them. They'll be looking to get to a final just as we are."