That can be difficult. When I feel myself getting impatient or angry or frustrated, I try to stop, step back, and breathe (as much as a Wall is able to do those things). Sometimes I need to focus on something else–something nice, like the trees outside the doorway, or something I am grateful for, like all the people who pass by and ask me questions. And sometimes I don’t succeed and am impatient with someone. (Not even the Wall is perfect.)
My friends say the more they can stay stress free and relaxed the less likely they are to become impatient. They recommend regular breathing–usually attached to some meditation or yoga. And staying healthy by eating and sleeping well and getting some exercise (maybe a nice walk around the reservoir). Listening to music–classical or whatever works best for you–can help in situations where you need to wait. Good luck; I think just by asking you are already on the way to being more mindful of yourself and your reactions.