I have a strong opinion about someone and I plan on saying it behind his back.
What do you plan to say about him?
He is bad when he is at the office.
Gossiping about someone else is not only rude but also possibly hurtful to feelings or damaging to reputations. People who don't feel good about themselves temporarily feel better when they judge others negatively.
It's trashy of him that he to smile in person but do nothing to me over the internet. He's such a sucker that I don't need to mind him.
I feel like you're trying to pick a petty fight and it's not going to be beneficial to you at all. I think you need to focus your mind elsewhere.