How do I tell a coworker that he sucks at his job and makes it harder for everybody else

Just like that..quickly and to the point..like ripping off a bandaid

Sounds like he needs some training

If it not your job to tell him he “sucks “ but it hurts overall performance. Your easy answer is collect opinion ms from coworkers and go ruin him.

A better answer is to help him along. Training is expensive and with some help he can change things.

Its not really for you to tell him directly. Voice your concerns to yr line manager.

"Hi Human if you do better at your job ill be your friend 🐰"

You: You should go be a prostitute.

Him: Why?

You: Because you suck

Put it on the table and hurt his feelings 😈 🐇 bad bunny

Just say it