I dislike, but only when I really disagree with the opinion, don't like the content, the content creator asked for a like/dislike based on if he/she should continue a new series, etc.
For example I sub to a guy who was a Call of Duty professional (like, played at tournys, guy is a millionaire from stuff on YouTube/CoD combined, retired now). He used to post a LOT of GREAT content for the competitive eSport scene.
Now he vlogs a lot, which isn't terrible, but he's not the best at vlogging. He posts a lot of crap that I think is just stupid and NOT AT ALL the person I subscribed to a couple years ago. He just seems to put crap content out now.
I dislike most of his stuff if I even watch it at this point because I honestly don't like the content he's pushing now, where I used to like the stuff before all the time.