I have been notoriously abused

So it's date night, and naturally my husband and I are at Borders. While selecting another book off the shelf in the writing and language shelves, I found a hardcover book called Why do We Say It?, a book of word and phrase origins that was only 7 bucks. I guess I was glamored by the bright-ass yellow dust jacket, or maybe the promise of blogging made easier, but I abandoned all sense and good judgement and threw it on the pile.
You'd think this would go without saying, but it's always a good idea, before buying a book, to check the author. Ideally, books should have an author or authors. If a book is a non-fiction book, it is sometimes helpful if the book sites sources. These are just a couple of tips from the Word Nerd to you.
You can't blame them too much for getting the origin of "OK" wrong, as the myth's a lot more interesting than the truth. The truth is that back in the 1830s, people made up slang abbreviations based on misspelled words for some freaking reason, and OK was short for "Oll Korrect." The myth is that the expression was an abbreviation for "Old Kinderhook," a nickname for Marten Van Buren. It's true that Van Buren took advantage of the coincidence in one of his campaigns, but "OK" predates that campaign.
What I cannot forgive the book for, however, is their origin for "tip." The book says, and a lot of folks say, that "tips" is an acronym for "to ensure prompt service." Well, first of all, the singular of tips is tip. Were it an acronym, the singular would be tips. Secondly, the word is ensure. Insure, though often used incorrectly, refers to insurance, as in "Please ensure that your car is insured." The actual origin of the term as it relates to a gratuity is murky, but there's no evidence at all that it started as an acronym, especially since acronyms are largely a 20th century thing.
At any rate, Why do We Say It? is, much to my dismay, like a box of chocolates, an unknown number of which have been poisoned.