A John is a person who is very annoying and a person who always complains about something to someone. He is also very gay and always steals the chances you or your friend get.
Perhaps there is a John in your class who is the like this you can use it as
You: Dude that guys a JOHN!
Your Friend: Yeah Dude!
A Name or a thing which is extremely beautiful.
That person is a Sidin.