This problem; me being stupid.

How would I go about making myself less of an idiot.

Be sure you can backup anything you say with facts and/or honesty. This is not a shield as you can be as intelligent as can be and some folks will still call you an idiot. Look at the what Nazi said about Einstein and as we all know, the Nazis were full of shit and then some. 

So, if the person calling you idiot is an idiot himself, then laugh and know you are smarter than they are. 

I don't know about him or her, but I got rinsed yesterday. Two pairs of sunglasses and two bottles of perfume. Thousand quid. Done.

Well, it's probably more a self-esteem issue with you Im guessing. No one is truly dumb imo unless you actually have a legitimate intellectual disorder.

All people fall into the trap of assumptions. It's just being human and a quick way to make decisions, probably an evolutionary benefit. However, some make more assumptions than others.

Just be curious and educate yourself on a variety of subjects. Read some books. Consume non-fiction material. No harm in fiction either.

You need to ask yourself why am I thinking this way? Sometimes you need to challenge your own foundations, the way you have been brought up, what you have already been taught, what you have been told etc

Also one can be smart in different areas. Some are better in socializing than others. Some are book smart. Some can have better common sense. Some can have technical/professional knowledge. Some are creative etc

Take for instance, a house. What kind of questions can you ask?

-is it actually a house? Could it be another kind of building?
-what is it made from?
-who built it? When was it built? what built it?
-how many people are inside? Are there actually people inside? Any animals? Even bacteria? Objects?
-which country is it in? is the land recognized as a country? Is it on Earth? Is it on the Moon? In the galaxy?
-How many windows? Are there windows?
-what kind of atmosphere does it have inside?
-are there secret rooms? Are there rooms? How many?

Anyway you can see where Im going with this. Just be curious and ask questions. You dont have to reinvent the wheel either. The internet can be a good source for the answers of basic questions. It gets more complicated further on

Lastly, you dont need to know absolutely everything either of course

Why don’t they exist? 

If you think aliens don't exist you are stupid POtatoe. Haven't you seen ET, or Close Encounters of the Third Kind?