When one of my colleagues went on vacation, he sent an out-of-office message that was both clever and smart. First, he sent the recipient on an imaginary scavenger hunt to "the highest peak of the tallest mountain." He used humorous absurdity to make it clear that he would not be checking email while he was away.
Meanwhile, I do sometimes put up long ones when I will be away for some days during a season in which there are a confluence of three or four very likely reasons someone would contact me, and who else they need to contact isn’t the same. Like, it’s high llama grooming season, and generally during this month I get two or three requests per week for each of llama bleaching (for which my backup is Stella), llama shaving (for which it’s Arturo), and llama perming (for which it’s Carter). My message says I’ll be out until blah blah, and if it’s not an urgent llama grooming issue, I’ll get back to you after that, but meanwhile, for urgent llama grooming here’s who to call.

Naturally, she had to take the day off — and couldn’t let folks know with any old generic auto-response. Instead, she made a guessing game of it in her out-of-office email, which you can use for yourself, below.
Who talks like that? A blowhard, that’s who… I promise, gentle customer, you won’t hear garbage like that from me. I’ll tell you why I like Aviation… Because it tastes like somebody finally made a gin for everyone.