For me, nothing major that come to mind. I'm able to tune out most minor annoyances. However, if it's bad enough to start distracting me, I'm not shy about mentioning it to the player and/or TD.
Annoying Habits At The Board...
It seems that a lot of young players cannot sit still at the board. I've had a couple of young opponents leave the board as soon as they make a move. In this day and age you cannot help but wonder if they've got an electronic device that they are checking every time they leave...but then again, maybe it is too much sugar in their diet.

I'm a habitual pen clicker. Anytime my brain is running I reach for a pen. Completely subconscious move. Most people point it out and ask me to stop. 😛
I try to carry pencils instead...

Whatever the opponent does doesn't matter to me....even if he dances naked in front of me I will still try to checkmate him with the same humiliation... As I wud do to a normal person...

Repetitive "pen clickers"...leg twitchers...throat clearers.....
The opponents we love to hate.
A team mate mentioned to me how his opponent was sucking a sweet that kept making a clicking sound against his teeth, and was driving him mad..
There must be a few stories out there ?
If youre focusing on the game, not much will bother you. I have kids, so i have learned to tune things out. The few times i have had an opponent doing something annoying, its been a kid, and its been done on purpose. I get the TD and that ends it.

Ha ha. I heard a story about what they did to stinky guys in the military. They would grab him in the middle of the night, and drag him to the showers, and literally scrub the stink off him. Needless to say they only had to do it one time.
I swing my foot, either one, like to an internal song. I also used to twirl my pen, or pencils between my fingers. sometimes rapping out a drum solo. lol. Never at a tournament however.
Repetitive "pen clickers"...leg twitchers...throat clearers.....
The opponents we love to hate.
A team mate mentioned to me how his opponent was sucking a sweet that kept making a clicking sound against his teeth, and was driving him mad..
There must be a few stories out there ?