What we need in our work communication is not more professional politeness or less formal, chat-based messaging applications like Slack. We need honesty. The problem is that we’ve conditioned ourselves to see honesty as self-indulgent or disrespectful. I’d argue the opposite is true. Honesty, even if it’s a bit more inconvenient for all parties in the moment, pays dividends later. It builds trust. When my partner Anne Helen Petersen and I were interviewing people for our forthcoming book on remote work, a frequent lament from both middle managers and workers was that they didn’t feel like they knew how to succeed in their jobs; that they were guessing what their superiors and coworkers wanted and, even when they asked, they didn’t quite trust the responses they got back.
Informal approach helps your clients think of you as of a human being. This alleviates some of the annoyance they may feel because of not receiving a proper reply. Generally, making people laugh is a great way to make people remember you. Do that and your clients won’t switch to a competitor.

That said, I think it is the kind of thing that is funny with the right people and in the right situation. But an out of office message is an autosend situation, so the email system cannot actually assess if it is appropriate or if the person receiving it will find it amusing, or unprofessional, or apparently even condescending. So while it is a hilarious message for a joke, it would not be a good idea in a professional setting!
Thankfully, with a simple out of office message taking a day off doesn’t mean that your communication with clients has to stop.