I'm quite tolerant, partly because I have a teacher's temperament, but also because most of my players spend a LOT more time playing than I do and I often have to lean on them for some of the more uncommon rules. About the only time I can be a bit impatient is with spell casters. I just don't have all the spells memorized. I expect spell casters to know what a spell does before they cast it.
Luckily, I have not been in the position of having to steer new players away from casting classes if that is what they want to play, because I have several players who like playing wizards and clerics and have memorized most of the commonly used spells.
What also helps is that I have a DnD Beyond subscription which gives all my players access to the core materials. It makes it easy to pull up a spell and look it over before it is your turn. I also have spell cards for the spells in the PHB and Xanathars which is helpful for some players.
I guess the only thing that annoys me is when players space out or get into a side conversations and don't take time to think through what they are going cast until the start of their turns.