I've only unsubscribed from a series maybe once or twice, or even deliberately chose not to subscribe to a series because I just didn't care for it. I believe I made this point in another thread asking a similar question, but one example of a series I subscribed to was one that ended up just becoming a "i'm dark and depressing and urgh" which was originally a funny comic and then just turned into . . . well, that.
Stuff that reads like teenage angst just sounds like frivolous complaining to me, and I don't enjoy reading that because it just makes me go "Well. . . uh . . . hmm . . . am I supposed to feel bad for this or react to it?" That's just me though, as I have a ridiculously low rate of handing out sympathy. It just pisses me off. That was like, the one rare occurrence where I deliberately unsubscribed. Haven't liked the comic since.
I basically don't want to read anything that's just a sappy diary. I read lots of comics already that are based on people's lives, but I read the entertaining ones that are based on people's lives, whether they're funny or silly or just make me smile. Comics that are built on "My life sucks, here's my depressing story" just turn me off big time.
Other than that, I haven't really unsubscribed from any other comics, so that's really my biggest peeve so far ^^^^
I'm guilty of this as well xDDD There are some comics I should actually unsubscribe from considering I haven't followed them in well, ever >.>