Backbiting is essentially talking about someone in a negative manner - hence the biting. The back suggests that you are not doing it to their faces, which means you are doing it in secret, behind their back. We only need to use our intelligence to know if it is evil or not. If you are saying something kind behind someone's back, then you are not biting them. A politician is different, because his job is to win or lose your approval - hence he/ we expect his performances to be judged. In many cases, this will have to be behind his back as we may never get the chance to meet him/her.
Talking and laughing about someone who is fat may not be backbiting but the Koran tells us not to talk about others in case they are better than us. He/she may be fat, but they may not laugh about other people because of their appearance and hence more righteous in the eyes of God, although, to stretch a point, God also says he doesn't like the gluttons - but that is up to God to judge, not us.
If you tell another colleague that someone is slow at their job that is backbiting. it is not for you to discuss with others. You may notice it, but talking about it may well bring negative reactions to your 'slow' colleague. Basically, I think one just has to use intelligence.
Peace,
Dawn.
