What is bad animation? The answers cannot be crystal clear. Why? Because animation, like painting or photography, is an art, an expression of the artist.
There are many ways of doing animation, for example, one would have to go about TV show animation and feature film animation differently as both use different methods of animating. Limited and full animation. Does making animation with less frames or less key poses mean that it is bad animation? Not necessarily. Japanese animation is famous for its animation techniques. Not being able to animate like a Walt Disney Feature film does not make you any less an animator. Lots of stop motion animation looks jerky, does that make it bad?
How would one begin to judge what is bad animation? If you look at every aspect of an entire film or TV show, maybe then you could form an opinion saying “Yeah that sucks because I didn’t like the way the character died”. But that is not referring to the actual animation, rather the story. When learning animation its easy to spot what you like and don’t like and what seems to break the reality of movement. And that is the point of animation – making movement. So if something in an animation is not making the viewer convinced that the characters are living, then is that bad animation? Or is it incorrect technique? Two drawn mouths for lip sync in Japanese Animation breaks reality, but does that make anime bad animation? Apparently not.
As long as you are convinced something is moving, you do not necessarily have good animation. The author is the first that should be convinced by his or her work. He or she must think that what has been created is really happening, not real but really. If the animator is not feeling it, then it is bad animation. If the animator is in love with the imagery, the movements and the plot, then it should work.
There is no clear way to judge animation. Everyone has his or her own opinion. I think that if the artist has managed to convey their message across to the viewer by means of a life-like character, one that the audience can fall in love with, they have succeeded to cross various barriers of bad animation.