Everyone has pet peeves, and I hold one in particular: Dice rolls in batches. Apparently, I'm not the only one who is annoyed by this, so I'm glad.
Two people I know roll 4 to 5 dice at a time in a shooting or assault phase that has 20 to 30 shots in it, so I have to sit down and record all their hits and misses and whatnot to prove that they're not cheating, then watch them repeat the whole process for the to-wound rolls. What takes almost a minute for them to finish, I finish in a few seconds. Game dragging, extra work for me, and ultimately annoying. Just roll those darn dice all at once! is what I feel like yelling at them every time they do that, and sometimes I do.