The name was originally used as an insult[1], however the followers adopted it, thus rendering the insult moot:

In 1650, Fox was brought before the magistrates Gervase Bennet and Nathaniel Barton, on a charge of religious blasphemy. According to Fox's autobiography, Bennet "was the first that called us Quakers, because I bade them tremble at the word of the Lord". It is thought that Fox was referring to Isaiah 66:2 or Ezra 9:4. Thus the name Quaker began as a way of ridiculing Fox's admonition, but became widely accepted and used by some Quakers

[1]: https://en.wikipedia.org/wiki/Quakers#Beginnings_in_England