Bozo

Bozo is a name that references someone who has failed to achieve any level of formal education and is easily lead and influenced by anyone who appears sympathetic. Bozo will, because of their lack of of understanding of the english language, try and engage in conversation, but in almost all cases, will become irritated and abusive due to not understanding what is being said to them. A Bozo will make up stories about their achievements, but everyone knows that they are just fabrications. A Bozo is not smart enough to know that their lies have been discovered and will continue on prosecuting the lie.

A person having very low intelligence aka being slow as fuck

is a very old clown. 1

also can be used to insult others 2

A bozo is one who writes definitions for urban dictionary.

A fluffy and lumpy dumb person who struggles through everyday activities like getting to work fully clothed and in one piece. Often used affectionately but with an eye roll. Said bozo typically wears tragically goofy footwear and has sleep in their eyes.

Someone who is intentionally irritating.

An incompetent person, especially in new companies. Bozos have a net negative effect on morale and profits, and everyone knows it.
I first heard this specific meaning of "bozo" during a talk to business students by one of Yahoo's founders.