不伦不类:neither fish nor fowl

四不象:david's dear

不三不四: dubious-looking

Examples:

1. 他和一些不三不四的人臭味相投。

He shares the same rotten tastes with some dubious characters.

2. 报上那些不三不四的文章使她对他抱有偏见.

Newspaper gossip had prejudiced her against him.