I like words where one kanji is changed to make the meaning opposite (without changing the pronounciation)

名演 (great acting performance) -> 迷演 (baffling performance)

国道 (highway) -> 酷道 (road in terrible condition)

There are also some horrible ones like 毒女(独女) and 害人（外人）

Also 休館日 (museum holiday day) -> 休肝日 ("give your liver a rest day" - i.e. sober day)