There are a lot of issues raised here and I'm going to take them in a different order than presented:
Is the idea of destroying your opponent's fun good?
Not in my opinion. From the perspective of winning the game, you seem to believe that denying them fun will lead your opponent to blunder. It may against some players. However, "battle-hardened veterans" will have seen players who use strategies like this and are likely to just play on with no ill effect. For some folks it is the winning that is fun. So if they beat you it doesn't matter what you did during the game; the only way to deny them their fun is to defeat them. Other people have fun just playing, so there may not be an approach you can take that will deny their fun. Thus I don't think this is a dependable method for winning.
Additionally, I will relate a story from my childhood. While I learned the game from friends at school, after a while I could no longer play there. As my family lived "out in the middle of nowhere", I had no one else to play (this was long before ubiquitous internet access) except two step siblings. They were the sort who couldn't enjoy a competition if they didn't win, but I quickly advanced past their skill level and defeated them every time we played. Thus I quickly found myself with no opponents. Unfortunately, this lasted for several years. So, making the game a miserable experience for your opponents could lead to having no one else to play. Of course, if you are better than they are and they are the sort who only enjoys winning, there may not be much you can do, except to teach them to be a better player if they are amenable to that.
I play for two purposes:
1.to win the game, or when winning is unlikely, to draw the game.
2. to improve my chess skills, which eventually enables me to win/draw more games.
Others have already pointed out that the second point is at odds with your proposed strategy of boring your opponents into blunders - you aren't improving your chess skills by taking advantage of opponents' blunders. Also, relying on mistakes by your opponents won't lead you to wins all the time, as you will encounter games in which the other player doesn't make (game changing) mistakes.
As for the actual title question about minimizing your opponent's fun ...
I realize you are primarily discussing on line play. I think that boring your opponent or making them unhappy in the game is harder when you don't even see your opponent, especially if it is someone with whom you are unfamiliar. If it's someone you have familiarity with, then you may be able to play openings they don't like or that are boring and avoid sharp lines. Furthermore, none of these are inherently wrong or necessarily going to induce boredom or displeasure. If you need a draw to win a prize, they are even quite understandable. What I really want to address under this topic is over the board play, where methods of denying can fun include:
- Sighing, cursing under your breath, and making other noises when you discover a mistake
- Similarly, saying "A-ha!", "Eureka!", "Gotcha!", etc. when something goes your way.
- "Smashing" the clock, especially if it is your opponent's and you do it particularly forcefully, making them think you might break it.
- Making your move and hitting the clock so fast that your opponent hasn't even had a chance to hit the clock themselves.
- Asking to see your opponent's notation sheet because you messed yours up. Double the annoyance if you do it on their turn/time on clock.
- Making all your physical movements as if you only have seconds on the clock, even if it is very early in the game or after thinking for quite a while.
As noted in comments, these actions could cause your opponent to register a complaint for distracting behavior that would lead to penalties.
when my opponent finds a game non-interesting, they will more likely make inferior or aimless movesmay lead to more wins (first goal), but how is decreasing the challenge going to
improve my chess skills(second goal)? Isn't it like playing a video game and choosing the "easy" setting instead of "hard"?