First I'd figure out why they are irate and if I can remedy the problem. Most people wont't continue to be unreasonable if someone is focusing entirely on their need, with a genuinely kind attitude. But, as I would not be disrespectful, I will not accept being disrespected. A polite suggestion that perhaps they'd like to come back when Ive found a resolution, subtley giving them the option to be more receptive to it.