Spinach in teeth could happen to anyone.  Flaunting of ignorance... well, it probably does happen to everyone, but I think "he who is convinced against his will..." applies.  What was the context?  Did he make this pronouncement to a group of people?  
Basically, if one wants to become the type of person to go about correcting people's mistaken notions about grammar, it's probably a good idea to have a book or two that you are then willing to stick to in the future where you can show people.  I happen to have a whole shelf where I could go and look stuff up depending on what the desired outcome of the conversation is.   :devil:   I'm just sayin'.  It's a rare argument that can be won with "Language is an organism; words are neither good nor bad, they simply exist."
Boy that last phrase was hard to put.  Also, I've never had to open a book with someone.  In general, the knowledge that I could results in people not questioning me much.  It's weird, because we question each other a lot here, because we're mostly languagey types, and hyperliteral ones at that.  In normal life, people find me scary.
Part of what I love about my job is that my boss is very literate, and I know that he values my skills.  I just realized that.