A person who always thinks they are going to die may be experiencing health anxiety, also known as hypochondria. This condition involves excessive worry about one's health and a preoccupation with fears of serious illness or death. Such individuals may frequently seek medical reassurance or interpret normal bodily sensations as signs of severe disease. If these thoughts interfere with daily life, it might be beneficial for them to seek support from a mental health professional.
Someone who doesn't have a life. If you meet someone like this tell them that they need to be more social.
A person who thinks highly of themselves is often termed as egocentric or narcissistic.
Atheist.
A cosmologist
Someone who constantly thinks and reflects on various topics can be described as contemplative or introspective.
A person who always thinks they are handsome may be described as vain or narcissistic. Such individuals often have an inflated sense of self-importance and may prioritize their appearance over other qualities. Additionally, they might be referred to as self-absorbed or conceited, depending on the context of their behavior.
Ignorant.
zen master
A person who thinks nasty things could be described as pessimistic, cynical, or having a negative mindset.
A person who thinks only of themselves is often referred to as selfish or self-centered.
A person who thinks big and has ambitious ideas is often referred to as a visionary or a dreamer. They may also be described as having an expansive or innovative mindset.
If a person thinks they are funny when they are really not, I would call that person a failed comedian, and possibly a fool. Or maybe the person lacks self confidence and that's the only way he know to bring attention to himself.