Is it considered hypocrisy if I treat an abusive colleague kindly and smile in his face despite my dislike for him, and should I confront him or seek my reward for that with Allah?

Allah has enjoined upon us to be good to neighbors and colleagues, and has forbidden backbiting (gheeba) and slander (nameema), which is the نقل الكلام (conveyance of speech) with the intention of causing corruption. Indeed, the slanderer shall not enter Paradise. What he did by conveying speech is forbidden slander. And upon the one to whom the slander is conveyed is not to believe the conveyor, nor to spy, but rather to forbid him and detest him for the sake of Allah, and not to think ill of his brother. Treating an evildoer kindly is not hypocrisy; rather, it is to ward off his evil. And he should be advised kindly, as long as no corruption or harm results from that.