When you're impatient, you can respond in many ways. You can mask your impatience and simmer in silence. Or you can do the opposite: Unleash your irritation, scowl frequently and throw up your arms in exasperation.
But the best option in most situations is to avoid throwing a fit. Instead, be assertive without getting pushy.
It's fine to alert others that you're not in a position to wait endlessly. By conveying that message in a diplomatic, non-threatening manner, you're more apt to get results.
The look on your face sets the tone for the conversation. If you smile slightly and speak in a compassionate or empathetic voice while you say, "I'm squeezed for time now. Can we wrap this up?," you reach out for a rapid resolution without sounding petulant.
Rather than speak through clenched teeth as you radiate stress, maintain your composure and show support for the person's predicament. Propose easy-to-implement solutions without sounding aggrieved.
If all else fails, ask sincerely, "What can I do to help you?" It's a disarming way to ally yourself with others.