Demonstrating Custom Validations to Prevent Specific Text

comment.rb

# Assumes a Comment model with a message attribute contianing the text of the
# comment. Change these to suit your needs.
class Comment
  validate :disallow_phone_numbers_and_email_addresses

  # possibly not the most performant, but it's clear
  # assumes you have arrays of regexes you want to dissalow
  def disallow_phone_numbers_and_email_addresses
    if PHONE_NUMBERS.any? { |regex| message =~ regex }
      errors.add(:message, "cannot contain phone numbers.")
    end

    if EMAIL_ADDRESSES.any? { |regex| message =~ regex }
      errors.add(:message, "cannot contain email addresses.")
    end
  end
end