By month six there's usually one. Waiting longer doesn't make the conversation easier, it makes the gap between expectation and reality bigger, and harder to name calmly.
The issue you've been avoiding didn't get smaller while you waited. It got a longer paper trail of you not addressing it, which becomes its own problem the day you finally do.
Name the specific pattern, not the personality
"These three deliverables missed the agreed date" is addressable. "You're not reliable" isn't, it's a verdict, not a starting point for change.
Check your own contribution first
Did you actually set clear expectations for this? Sometimes the fix is a conversation about clarity, not a performance conversation at all.
Use the script, don't improvise
This conversation goes sideways most often when it's freestyled under pressure. Know your opening line before you sit down.
Set a real timeline for reassessment
Not "let's see how it goes." A specific date, and a specific bar for what changing looks like.
Example
A designer on your team has missed the last three deadlines. You've mentioned it in passing twice, and nothing's changed. Waiting for a fourth miss doesn't make it clearer, it just adds another data point to a pattern you already have enough evidence for.
Use the script
The Performance Conversation Script covers exactly this conversation, line by line.