I think one of the other issues here is that people are too afraid of hurting someone's feelings. If someone sucks, they suck. No way around it. Instead of coddling them, telling them that they're the best thing since sliced bread, tell them that they suck. Don't lie to them about it; that's the worst thing to do. They should accept that they suck and try to better themselves. All these terms for "stroke" are basically just saying that someone sucks at diving, and they're most likely a potential hazard to themselves or others.
If someone tells you that you suck at diving, or calls you a stroke (or whatever else), ask them why they say it instead of refuting it immediately or calling foul. If it's a valid concern, try and fix it. Many times, divers don't know what they're doing unless they see it on video. They'll deny it like you wouldn't believe, until they watch themselves do it.