【成语来源】 

be tarred with the same brush
狼狈为奸

A wolf and a jackal often went hunting together.
狼和狈经常结伴去伤害牲畜。

Once they came to a sheepfold, the walls of which were too high for them to get over.
有一次，狼和狈一起走到一个羊圈外边，栅栏很高，进不去。

Then the wolf stood on the back of the jackal. In this way the wolf climbed over the wall to where the sheep were.
狼就骑在狈的身上，终于爬进了羊圈。

This idiom is used to describe doing evil things in collusion with others.
这个成语比喻坏人相互勾结起来做坏事。

【文化链接】

“be tarred with the same brush”的英文解释是“sharing the same characteristic(s); having the same good or bad points as someone else.”（有着某种好的或者坏的共同点），所以它既可以表达“狼狈为奸”这样坏的意思，也可以单纯表达“有着某种共同的优点”这样好的意思。

这个短语的由来可能与“tarring of sheep”这个说法有关，牧羊人为了区分自己的羊，就会在羊身上用刷子刷上不同的标签以示区别。所以当说“两个人被同一个刷子刷过”也就是比喻“两个人狼狈为奸，或者有着共同的优点”。