I understand emergencies and don't mind waiting if that's the case. At my doctor or the vet office.
But just last week I went in for my annual "lady" exam. I got there on time for my appointment. Went into the room and put on the paper thin robe and sat on the table with the paper over my lap. On my way to the room I saw my doctor sitting at her desk on the computer. I sat in that freezing cold room with basically no clothes on for almost 30 minutes before she came in to see me. Now I may not have been so irritated if she (or someone) had popped their head into the room to apologize and let me know they didn't forget about me and that they'd be with me soon. The exam only took about 20 minutes. Would have been less if I hadn't had some other questions.