Yeah I was going to say, I have a friend who sometimes will turn a card upside down to indicate which color he is playing if he is seated next to one of us. The idea being if we avoid his color he will avoid ours in return.
I don't mind moderate hand shuffling as most of the time it just makes them look like they have ADHD. I think it's funny that most of the kids are just doing it because they think it's what the "pros" do. Excessive hand shuffling though is obnoxious as fuck. It's clearly done to be a distraction and to throw the opponent off their game, which makes me surprised that it isn't frowned upon by judges. If someone was sitting there making animal noises repeatedly like meows or bird chirps for 30 minutes straight non stop, I'd think a judge would come over and tell him to knock it off. But maybe there aren't any rules about disruptive behavior of that nature.
Far more annoying to me though is when players excessively shuffle my deck in an meaningless event. I was at a 8 person draft at some shithole comic shop we weren't even sure was sanctioned. With my first opponent, after placing my deck in front of him, he would shuffle my deck, then pile shuffle it, then shuffle some more, pile shuffle again, cut it, shuffle some more, and then pile shuffle a third time before giving it one last shuffle. He did this every single fucking time. I ended up stomping him too so the goddamn shuffling took longer than the matches. And just to rub it in like a dick, I never once cut his deck or shuffled it.
A friend pulled a Temporal Mastery and a Griselbrand but nothing else notable outta our box.