"I do not want to work with you because of reasons A, B, C." Leaving out the reasons would also be ok, but don't be surprised if this results in confusion and

"I do not want to work with you because of reasons A, B, C." Leaving out the reasons would also be ok, but don't be surprised if this results in confusion and anger. (However, the abusive alternative to this will likely not help reducing the confusion or anger.) "This work is bad because of reasons A, B, C." Leaving out the reasons would also be ok, but don't expect other people to agree with you if you do that. Being straightforward doesn't require one to be abusive.