What makes a cold outreach message read as "AI-written" to you?

Genuinely asking, not rhetorically. I've read a lot of AI-generated icebreakers lately, and the tells aren't always what I expect. Sometimes it's over-complimenting ("Your impressive work at X really stood out!"), sometimes it's just too smooth/no friction, sometimes it's actually fine and I only know because I was told it's AI.

What's the actual tell for you when you read a cold message? And does it matter if the content itself is accurate and relevant, or does the "feel" ruin it regardless?