Like this bird for example:
Don't worry though, this picture is photoshopped, birds don't usually have teeth.
If you thought this bird is scary, wait till you see this next one!
The fabled dragon. Personally, its the scariest bird I can think of, and couldn't be happier that it doesn't exist. I remember watching Reign of Fire (2002) and being scared half to death thinking about how much it would suck if dragons really existed. It was one of my first encounters with a dragon on the big screen and man was it a powerful one.
How To Train Your Dragon (2010) was a much more kid friendly dragon movie that tried to break the mold of dragons being terrifying and put a delightful twist on it. The movie focused around a boy who befriends a dragon only to realize that dragons have been sorely mistaken and are actually very nice.
Although the movie does a great job in helping the audience sympathize for dragons, I still think the world would be a lot worse of a place if they actually existed.