I saw a version of this on IG that was an old school (paper) OOO from an associate pastor. It has a line like “if this is an emergency and you must speak to someone, Jesus is always available on the mainline.” Too funny.
The boss’s thinking was that people who did drivebys looking for you would then email you, see your OOO, and then be able to call you to talk about whatever they were driving by for. No one liked putting their personal contact info so we never worked from home (pre-COVID and pre-VOIP implementation) or told people to IM us and we’d call them.

I might sound nitpicky but the language is important. “Might” or “may be” or “slower than usual” are vague and don’t offer the sender all that much information about when you’re really going to respond to them. Worse, they do a horrible job of protecting the time of the email receiver who, as the responder notes, is not in the office! Such a responder implies that, not only will the vacationer reply to the email, but they may not even miss a beat. They may be slow to respond, but they also might not.
People also hate it when some people sign “Sincerely,” but also a bunch of people hate “Thanks” and “Best” and “Toodles” — almost any signature you pick someone will hate. This is one of those areas of language that feels really subjective and culturally dependent and also…isn’t that big of a deal?