Very little pisses me off like downloading a ‘free’ app and immediately being hit with a paywall for a subscription without so much as a free trial. Those devs can go fuck themselves. Their app is NOT free and should not be marked as such.

Alternatively, shit like what Accuweather did also pisses me off. Years ago, they had a one time payment to remove ads permanently. I paid, because I like their service and didn’t mind kicking a few bucks their way to support development. A few months later, they introduced a sub model that locked many existing features behind a wall and started showing me ads again. I immediately uninstalled that shit, sent them a scathing email (which I recognize does nothing, but made me feel good), and found an alternative.