profanity.rb

# Option A: I'd start with this
class Micropost < ActiveRecord::Base
  validate :no_profanity

  private
    def no_profanity
      if user.minor? && profanity = profane_words_used_in_content
        errors.add :content, "Profanity: '#{profanity.join(", ")}' not allowed!"
      end
    end
    
    def profane_words_used_in_content
      content.split(/\W/).select { |word| word.in? Rails.configuration.x.profane_words }.presence
    end
end

# config/initializers/profanity.rb (using custom_configuration gem)
Rails.configuration.x.profane_words = %w(
  poop
  crap
)



# Option B: If you are going with an external class, at least use the validation framework
class Micropost < ActiveRecord::Base
  validates_with NoProfanity
end

class NoProfanity < ActiveModel::Validator
  def validate(post)
    if post.user.minor? && (profanity = profane_words_used(post)).any?
      post.errors.add :content, "Profanity: '#{profanity.join(", ")}' not allowed!"
    end
  end

  private
    def profane_words_used(post)
      post.content.split(/\W/).select { |word| word.in? Rails.configuration.x.profane_words }
    end
end