When your brain can't comprehend easy things, such as a simple joke . You will not have good ideas and your shower thoughts are lame as hell. People dislike you for unintelligent mind and call you stupid for your misinterpretation on things. You will use big words to make you sound smart. As an example, I am smol brain.
" I wish I had a big brain, but yet I have a smol brain.
A day when you rest from school, and potentially become smooth-brained, also known as the day of idiots.
Person 1: Hey, what’s Obama’s last name?
Person 2: -_- How smooth brained can you get on Smol Brain Friday? Obama is the last name.