It's just a matter of connotation, isn't it?

Generalisations are all well and good when they suit, but it seemed as if you were going rather farther than necessary bring those generalisations associated with Slytherin to light. I wouldn't say that "sneaky" has a particularly positive connotation.

I've never noticed you do anything like that before, but some of the girls are trying quite hard to get the attention of visiting students, and in quite inventive ways.