He brazenly played with his phone in class, ignoring the teacher's warnings.

brazenly 是副词，由形容词 brazen（厚颜无耻的、肆无忌惮的）加上副词后缀 -ly 构成。brazen 本身源自 brass（黄铜），比喻像黄铜一样厚脸皮、不知羞耻。brazenly 表示"厚颜无耻地、明目张胆地"做某事。