"That's just wrong!"
I usually see this used when people encounter something that isn't necessarily bad or hurtful to others, but is, at worst, unusual. I've heard this phrase used in response to the fact that there are grown adult males who watch My Little Pony, the existence of bondage fetishes, odd piercings, and many other things besides. I've even had it directed at myself for still playing Pokemon at my age.
I hate the phrase not because they disapprove of these things, but because they never provide a reason for their disapproval. They just indulge their knee-jerk reactions, with no thought as to whether or not something is truly "wrong", or if it's actually having a negative impact on anyone.