I read an article in Business Insider, "Nine Signs Your Co-Workers Think You're Dumb." This list is partially inspired by that article, and very much inspired by my own experience. I have come up against many of these, not just with co-workers but with people in general. As a mental health consumer, I might even find case workers who act this way toward me.

Can anybody think of anything to add to the list?

And possibly more important, does anyone know how to stop giving off that vibe, so people don't act this way?

Here is the list I've compiled:

1.) They don't seem to trust what you say. They argue with it, question it, doubt it, disregard it, and have to hear it from another source before they accept it.
2.) They roll their eyes and/or sigh when you speak to them.
3.) They laugh at things you say, although you weren't trying to be funny.
4.) They don't ask you for help, and won't accept it when you offer.
5.) Conversely, they're quick to jump in and overhelp you when you didn't ask for it. They may even grab something right out of your hands and do it for you. (I had opened a hymnal at church. The words were on the wall, but I didn't know the melody, and I can read music. I had barely started looking when a woman near me actually took it out of my hands and found the page for me before handing it back. I don't know my numbers, right?)
6.) They interrupt themselves to define words for you, even though you didn't ask what the word meant.
7.) They repeat the same bit of simple information several times, to make sure you "get it." Then a few minutes later, they write it down for you, "just in case." (Not only are they not trusting you to remember, but they're even suggesting that they don't think you can write it down for yourself.)
8.) They tell you obvious facts that most small children know already. (I've had people tell me as an adult that milk sours when it's not refrigerated, that helium balloons float away when not tied down, that a hot iron will burn me if I touch it, and that what's going on in a sitcom is acting, not reality.)
9.) They speak to you in a high-pitched voice with short words and sentences, call you terms of endearment like "honey" and "sweetie," and/or use baby-talk terms like "go potty" when they don't speak this way to others.
10.) They frequently compare you to people or fictional characters who are known to not be very bright. (Forrest Gump, for example.) If asked what they mean by that, they'll be dismissive and say they're "just joking."
11.) They lie to you and think you won't know the difference. They'll categorically deny doing anything on this list, even though they're clearly doing it.
12.) They don't invite you to join them, and make up excuses if you invite them.
13.) They assume you're probably new at something you've been doing for years, or that you probably can't do something before they've even seen you try. (I've had people assume without asking that I'm unable to drive, and they're stunned when they find out I can.)
14.) They're quick to give up on you. They point out your every mistake before you've had a chance to correct it yourself, and then they don't let you try again.
15.) They act surprised when you succeed, and/or groan and say "I knew it" when you don't.