It seems the OP is asking about how to describe a “bad” piece of art. There are several options.
Gauguin titled the work Where do we come from? What are we? Where are we going? Although he expected critics to dismiss this painting as poorly executed, Gauguin declared, “I was so bent on putting all my energy in it… ,
7 mistakes that make your paintings look amateurish and why some people
don’t even know their paintings look amateurish
The following word refers to how badly the paint is applied in a painting
n 4. A crude, amateurish painting or picture.
American Heritage® Dictionary of the English Language
n 4. (Art Terms) an unskilful or crude painting
Collins English Dictionary
From Judging the Image: Art, Value, Law by Alison Young
In the register of art criticism, ‘daub’ has strongly pejorative meanings. Calling a painting a 'daub' would indicate dislike for the work, criticism of the artist's abilities and condemnation of the effort applied to the work. ‘Daub’ derives from Middle French and connotes the act of coating with soft adhesive matter such as plaster, coating a surface with dirty substance, and applying or smearing colours crudely.
A daub, even if it is signed by Poussin or Picasso, will still be a daub.
The universally panned portrait of Queen Elizabeth by Welsh artist, Dan Llywelyn Hall; the commissioned painting was “criticised by many as being a 'hideous cartoon'” and resembling a ‘drag impersonator’.