Not all of them. The teacher in third year was a very good teacher, but he had to quit - or decided to quit - once the students (and their parents) found out some details about him. The teacher in sixth year knew his subject very well, but simply had a nasty personality. The worst dark art teachers were probably the one in year 2 (who didn't know much of the subject, although he claimed that he did), and the teacher in year 6 (who taught only very basic stuff, due to some unfounded fears by the Ministry of Magic).
One, in Defence Against the Dark Arts because of the DA
limgardiean leviosa
Gilderoy Lockhart was the Defence Against the Dark Arts teacher in Harry Potter and the Chamber of Secrets.
One's name is Alecto, and the other is Amycus. They are brother and sister twins and they are both death eaters who take the places of the muggle studies teacher and the defense against the dark arts teacher.
Dobby the house-elf told Harry Potter about it and said it was the perfect place for Harry Potter to teach Defense Against the Dark Arts to the DA group (Dumbledore's Army).
One, in Defence Against the Dark Arts because of the DA
Yes, Harry Potter contains black magic (Called Dark Arts in the book/film).
The first defense against the dark arts teacher in the Harry Potter series is called Professor Quirrell.
limgardiean leviosa
Amycus Carrow, a Death Eater, is the Defence Against the Dark Arts teacher.
Defense against the Dark arts
the defense against the dark arts teache
In the seventh book subject Dark Arts is taught by Amycus Carrow.
Amycus Carrow. Although it was more of a Dark Artsclass.
Gilderoy Lockhart was the Defence Against the Dark Arts teacher in Harry Potter and the Chamber of Secrets.
Arithmancy. Hermione takes this class, but Harry does not so we never actually meet Professor Vector.
Gilderoy Lockhart played the Defence Against the Dark Arts teacher, in Harry Potter's second year at Hogwarts (Chamber of Secrets).