tar someone with the same brush idiom
认为（某人与另一人）是一丘之貉
to think that someone has the same bad qualities as another person
Because they worked so closely in the same department, John was tarred with the same brush as Tim. 由于在同一个部门有密切的工作关系，约翰被认为跟蒂姆是一丘之貉。