Personally, I'd call the person wise. Really depends on the Reason Why the person is observing others. A person gaining wisdom would most likely observe wisely, meaning the person being observed wouldn't even know, but not to the Extreme. But a person just excessively watching someone, like staring, would be uncomfortable...Basically your question is unanswerable, unless you're more Specific.
Because they are dating one person then go behind there back with another one that is why we call them cheaters.
A person who makes people happy can be referred to as a joy giver, happiness spreader, or simply a positive influence.
you call all those people meaners. this means your just a mean person that likes to laugh at people.
You could call this person a "selfish immortal."
They are called egomaniacs. Mostly people fooling them selves about their worth.
He observes what the other dogs are doing.
He observes what the other dogs are doing.
sommeone who hidding someting __ Vigilant or alert
hero
hypnotist
@ssh0le.
A zoologist
a plagiarist
A Medium
A namesake, if one person was named for the other.
An examiner is one who tests others.
A person who tortures and gets enjoyment out of it is called a sadist.