I signed up for a new account on a fitness website yesterday. They track health and food and diet you enter. anyway, during the sign up they had a opt out, I chose to do just that, however the opt out process then took over the screen with a modal window, which gave a loading bar and took about thirty seconds to complete... But guess what... There was a big CANCEL button. I couldn't perform any action during sign up and opt out.
This was one of the worst dark patterns I've seen. PS. The app was MyFitnessPal which i registered on recommendation but that felt so shady.