"How can I tell my Partner that the guy he is interviewing next week is a completely wrong choice for the company?"- you can mention to your Partner that you know this candidate personally and would be happy to provide feedback during the hiring process. That's it."Can I be straight?"- depends on your relationship with this Partner. Probably not, as personal feelings count for nothing if has a useful skillset / network. You may think your ex-housemate is a backstabbing tool and he may think the same of you. If I were your partner I would take your feedback on board and while I may not hire this guy, some of the negativity will reflect on you as well. As EC says put NOTHING down on paper, but also couch your language in the most professional terms. "his interpersonal skills are couterproductive to a conducive team working environment. I think it is worth bringing out, although he may not eventually get through, but considering the companys desperation, I think he may"If the company needs his contacts / skills badly enough they will hire him even if you warn them of blood falling from the sky, wild animals attacking etc. Unless you are the hiring partner, ain't nothing you can do about that. If you still feel strongly enough to register your opinion, do it ONLY to the partner and don't use emotional words (I feel, I believe). You'll sound petty.