What is the person called who always thinks negative? E.g.
- Mr. X always thinks negative.
- Mr. X has negative attitude.
What we can use either? Is there any particular word for this?
The word is pessimist, a person who expects the worst.
Mr X is a pessimist.
Contrast with optimist.
It is often said that while optimists are happier, pessimists are more often correct.
and
Optimists are said to live longer than pessimists, though a pessimist might say those extra few years are bound to be miserable.
There are a lot of colloquialisms and other terms that mean the same thing:
"Mr. X is a ..."
'Mr X Thinks negatively' is correct.
However, 'Mr X is a pessimist' is more grammatically sound.
I've always enjoyed slang expressions like "Mr Unhappy is a real stick in the mud" (i.e. won't participate) and similar expressions like curmudgeon or party pooper. They have slightly different connotations than always thinking negatively, but I think the mindset would have the be similar to support them.
A lackadaisical person is someone who is listless and lacking vigor or determination, in short someone with a negative attitude.