Way too long, but so hilarious. I don’t get condescending at all. I’m drooling while imagining I had this on my work phone when everyone thought their requests were life or death. Actually, I wanted my message to say, “I realize you think your request is vitally important, but I’d like to reassure you: I worked in a hospital years ago, and good news! It’s really not.”
For those of you arguing that entrepreneurs and salespeople must always be available, I present to you Exhibit A. While this is specific to Yesware (and you should check out their other OOO examples), it's easy enough to tweak to fit your industry.

For example, if you don’t clearly state the dates you’ll be gone, your office coworkers and clients might send you multiple emails, clogging your inbox and making it difficult for you to catch up when you're back. And if you don’t include the name and contact information in your outgoing message for the coworkers who can help in your absence, your well-earned vacation time might get in the way of ongoing projects at the company.
I hope this email finds you well. I’m out of the office right now but will get back to you as soon as possible. Expect a reply next Monday. For urgent matters, you can email or call [Name] at [email and phone number].