I think... (my own opinion) it works like this:
Let's say you absolutely HATE playing against (or with) a particular champion. For example, we'll pick Amumu (He's already sad). If you consistently ban Amumu in every game you play, some people might get mad (if they hovered him) but the fact of the matter is you're not trying to ruin anybody's fun or anyone's day - you simply hate playing with or vs Amumu. You may get reported once in a while from the angry Amumu main, but I don't think you'd end up being punished just for banning the champion.
On the other hand, lets say you always ban the champion your Mid-lane is hovering. Doesn't matter of they hover Syndra, Zed, Yasuo, or Darius. If they're going mid, and they hover a champ, you ban their champ. You're purposely pissing people off every match. That, IMO, will get you punished eventually.
Just my take. I could be wrong.