‘不 + adjective’ can be in a negative imperative sentence, but not in a positive one.
别不识相，他不欢迎咱们，咱们走吧！
Bié bú shí xiàng ，tā bú huān yíng zán men ，zán men zǒu ba ！
Don’t be clueless. We are not welcome here. Let’s go.
别不好意思，上来表演一下吧！
Bié bú hǎo yì sī ，shàng lái biǎo yǎn yī xià ba ！
Don’t be shy. Come up here and perform (a song, a dance, etc.)!
[1] Yip, P. C., Rimmington, D., Xiaoming, Z., & Henson, R. (2009). Basic Chinese: a grammar and workbook. Taylor & Francis.
