in one's face是指针对某人.例句：Tom have write to the public in my face.汤姆针对我给新闻界写信了.
to one's face是“当面的,公开的”.例句：The manager said that the company is difficult to operate in every employees' faces.经理当着全体雇员的面儿公开表示公司最近运转困难.
希望能够帮助到你!有什么好方法记住这两个区别呢？这个其实真没什么方法。毕竟语言就是扎实基础一步一步走的，该背就得背牢，没有什么很大的捷径可走。