Name the problem, not the person. “The project’s late” gets fixed. “You’re lazy” gets fought.

Attacks on a person and descriptions of a problem produce opposite responses. Naming what is wrong leaves everybody facing the same direction with something they can do. Naming a character flaw puts the other person to work defending who they are, and nobody has ever fixed a deadline while doing that.

Strip the person out of your next complaint and leave the fact standing. Say the shift is short-staffed rather than that your coworker is useless. You can be completely direct about what is broken and still leave somebody their dignity, and that combination is what actually gets things changed.