me too i find myself sometimes in such situation . i think the best solution is to work, because when you make yourself occupied you don't think on silly things. it's preferable to do something that you really love; reading a book, learn a foreign language, meet a friend, see an interesting documentary,about nature it will relax your mind, anything you are interested in. by the way, try to practice your english or help others to learn your language. being usefull can make you happy a_a

"To kill time" means to make it pass quickly. For example if you are meeting someone at 6pm and it is 5pm what do you do to make the time pass quickly. You are killing time.