If someone eggs me on to sub to their channel, I'll hop on, sure; but that sets a low bar for my unsubbing. I often unsub from people who bore me, or have consistently produced content that I didn't care for. The most egregious event, however, is if they start promoting some sort of harmful ideology that I directly disagree with -- although if they actually interact with me, I'll try to talk to them first, but there's no reason that I want to listen to someone going on about something I find socially harmful.
Beyond that, really, being bored constantly by videos or finding myself dreading looking at their videos is often enough for me to ditch them.