People don't like the way the writers just declared Cho "the seventh smartest man on Earth".And indeed, that was later explained away as a soap company contest.
"Later"? It was in his first appearance that brought in the soap contest.
My reason for disliking Cho is his arrogance, and certainty that he's always right, when he's left almost the same level of human wreckage behind him that Hank Pym has. That arrogance might be interesting in a Tony Stark... coming from a kid, it's annoying.