If you make yourself an ass, don't complain if people ride you.
人善被人欺，马善被人骑。
活学活用：ass
ass in grain
十足的大傻瓜
play the ass
作糊涂事; 出洋相
an ass in a lion's skin
气势汹汹的胆小鬼; 色厉内荏的人
