答案：smoking.
翻译：大多数人们介意/在乎/反对在公共场合抽烟（的行为）.
固定短语mind (doing) sth,意思是“介意/在乎/反对(做)某事”.
再如：Everyone minds being laughed at in public.
每个人都介意在公共场合被人嘲笑.