Being asked to judge co-workers on their performance is a relatively new workplace phenomenon.
At the same time, what’s not at all new is that few of your fellow humans enjoy having their performance judged, particularly when there’s room for improvement. Even people who go out of their way to ask you for “a critique” are often, deep down, really looking for praise.
Meaning that it’s always wise to proceed with caution when offering feedback, whether sought or not.
First, you want to be clear on your own motivations. Never criticize someone just because you’re in a bad mood or as a way to make yourself feel more powerful. That your intention is to support and serve should be apparent to both of you, from the start.
Focus on one issue at a time. Bringing up a laundry list of problems can be overwhelming and may feel like an attack. We all tend to feel negative remarks much more keenly than positive ones, so keep in mind that your words may be burned in your colleague’s brain forever.
Criticize the behavior, not the person. Stress that you’re both on the same side. Describe how resolving the issue will benefit the workplace as a whole, including the person sitting right in front of you. Try to listen as much as you talk.
You can employ the classic “criticism sandwich” (start off with praise, hit them with the criticism, then go back to praising again) but this approach has become so commonplace it may have lost some of its effectiveness. Absolutely throw in some praise though. You don’t want the conversation to be solely about what the person is doing wrong.
Be specific. Framing your approach in a spirit of friendly collaboration, describe a few actual examples of the problem behavior and the bad result they led to.
Be timely. Don’t wait too long after a problem behavior has occurred to mention it — otherwise the person will wonder why, if it’s such a big deal, no one has brought it up sooner.
Finally, make any suggestions for improvement concrete and doable. Don’t just say, “You need to start pulling your own weight around here.” Mention a few specific contributions that the person might start making today.