Magician's thinking is a term I heard awhile ago and it refers to when a magician can longer think like a spectator. And it's bad because it always leads the magician to treating spectators like idiots. Usually it comes up in relation to non-rider back cards as in this rant, For those that don't want to read that rant it boils down to magicians with magicians thinking forget that there were other decks of besides Rider backed Bikes available to them before they took up magic. It's not too bad a problem in that situation beyond that it means the performer is avoiding some questions about his performance character. It's unlikely that in that situation that spectator will know that the performer is using bikes because they think the spectator is too ignorant to know other decks exist.
But recently I read a blog post on the Merchant of Magic blog, that told people to not use the word Sharpie because it was a magician's word and using would confuse a spectator. As I pointed out on that blog, Sharpie is a brand name of a widely available permanent marker. I'd go so far as to say that it is America's favorite brand of permanent marker. At least here we've reached the point where we call all permanent markers Sharpies. Much like all adhesive bandages are Band-Aids, or all whipped cream is Cool Whip. I know cause I'm that kill joy that will point out when it not the brand name brand and someone asks for it. Beyond the idea that the word Sharpie is some sort of magic jargon, saying not to use a word because a spectator may be unfamiliar with it implies you consider them too ignorant to know what you're saying from the context. Let's say we have situation where a spectator really has had no previous experience with the word Sharpie and you ask them to sign the card with a Sharpie. They know they need some form of pen to sign with and chances are the magician is holding out a Sharpie, it doesn't take a great mental leap to figure out what they need to do and that this marker being held out must be a "Sharpie".
It's like the golden rule thingie, treat others the way you want to be treated if you wouldn't want someone treating you like you were completely ignorant then don't do it to others. At the very least people tend to act how you expect them to act. If you expect them to be intelligent you may just find them rising to the occasion.