听洋葱没事吃洋葱我哭了
[tīng yáng cōng méi shì chī yáng cōng wŏ kū le]
Roughly translates as 'Listening to onions does no harm, eating onions makes me cry.' Perhaps it plays on how listening to something sad can affect someone deeply or subtly like hearing about onions, while actually dealing with issues (eating the onions literally) causes more evident reactions. It may also be a literal description where the person has cried from chopping onions.