Dozens of people have asked me some version of this question over the past few days. Here are some ideas…

1. Remember, you may be wrong. Make sure that when you criticize people you aren’t giving them the impression you’re 100% sure you’re right. Remember, a challenge is an invitation to fight back. You are saying what you think, so that they can either correct your thinking, or you can correct theirs. And if you are wrong, cop to it loudly, theatrically. I used to have a 2 foot tall “you were right, I was wrong” statue.
2. Take the time to explain why you are telling them this–to be helpful. If you can, offer actual help. Ask yourself, am I part of the problem or part of the solution here? If you are part of the problem, figure out how to be part of the solution.
3. Criticism has a short half-life. Give it immediately. If you are talking about something that happened a few months ago, the other person is going to start wondering what else you’ve been hanging onto all that time.
4. Have the conversation in person. This allows you to see body language–crossed arms, flushed faces, grinding jaws, and whatnot will let you know how the other person is reacting emotionally. Your job is not to control other people’s emotions–but you can react to them positively. “I can see you’re upset–I’m sorry about that. I know this is hard/frustrating. I’m not saying this to upset you or because I want to be a jerk. My goal here is to help you XYZ.” (Back to point 2) You can also ask, “Is there a way I could be handling this better?” Sometimes giving the other person an opportunity to criticize you can be productive. Sometimes they’ll lash out. That’s OK. If you react calmly/forgivingly to their lashing out then it’s a bit harder for them to call you a jerk.
5. If you are criticizing a person, as opposed to debating an idea, you need to do it in private.
6. Do not personalize. There is no point telling somebody they have an intractable personality flaw…

The first and the last are probably most important.  A successful advisor to some of the world’s largest tech companies once told me he totally turned his reputation as an asshole around when he learned to say, “I think that’s wrong” instead of “You’re wrong.” The “I think” was humble and saying that instead of “you” didn’t personalize his criticism.
Above all, do not allow being called a jerk to push you towards Ruinous Empathy!! When you’re the boss and you’re Radically Candid, it’s almost inevitable that somebody is going to call you a jerk when you are just trying to do the right thing. It’s part of the reason why I say that the relationship between a boss and an employee is a pay-it-forward, lonely, one-way street. You can’t measure your success by your popularity. You have to listen to the criticism leveled at you–but you also have to be strong enough to say, “I reject that feedback.”