I have had similar issues with dueling, even though I haven't played that mod very much. I tend to find duels very stressful. The couple games I've played against skilled players have left me feeling completely impotent, unable to accomplish the most simple of things. My palms get sweaty, my heart races...but it does make any minor accomplishment seem that much sweeter (air rocket, nice combo etc..). I think people tend to take duel losses more personally than other game types because there is no one else to blame but yourself I feel the same way about loosing a duel that I do about loosing a game of Chess.
I'm new to duel (less than 300 played) but the depth and difficulty is what has me interested in the first place. If I could beat players with more experience than me so soon then that would mean that the game has no depth because I'm certainly not naturally talented at videogames and I might as well play something with better graphics.
I know before I hit F3 against better players that there is a good chance that I won't be able to score more than 2-3 frags if I'm lucky. I just focus on timing at least one item, learning positions, where they're probably going to show up, trying to be as difficult to kill as possible, etc.. When I get stomped, I've still added 10 more minutes of experience to my game. If they're being a whateverwordisntcensoredhere about it, then I just turn off chat and they can spam their binds to themselves, and I've still added 10 more minutes of experience to my game.
Also keep in mind that whoever demolishes you also gets demolished by better players and so on until you get to the pros who demolish each other. k1llsen absolutely mauled Evil on his stream earlier for example and Evil frequently mauls others.
Try to ask you opponent for advice or to point your mistakes. If his answer is rude, then you'll have semi-legitimate reasons to insult him if not - you might actually profit from it and hopefully improve.
Real life? Life is real?!