Ron O'Neal was hardly a great actor in his day or at any other point. The core of his career was in Blaxploitation films. This line is hardly different from any of his on screen rants. He did the same thing in Red Dawn and When a stranger calls. Combine those monologues with his dialogue in the Superfly movies and well I don't see how anyone can expect that much.
You are taking a dump and they call GQ do you pinch it off or finish your business?

The worst acting by far should be credited to Ron O'Neal and the scene when the ship's top officers and Martin Sheen's character are trying to figure out the time paradox. O'Neal has this long tirade over the whole meeting and it's absolutely excruciating to watch he's so bad.
"For Christ's sake, what is this, some half-ass Princeton debating society? We are in a war situation. This is a United States warship, or at least it used to be. Or will be. Or what the hell ever. Oh, goddamn it, you can drive yourself crazy trying to think about this stuff. - Jesus, I must be dreaming!"
Ok, admittedly the line is pretty awful to begin with, but you can see the other actors in the scene realize how bad he is - particularly Kirk Douglas who more or less pats him on the head and shuts him up. I can't believe this is just an accident. This is probably the best take the director got of this scene and had to use it.
I point this out, because O'Neal at least is supposed to be an experienced actor who should know what he is doing. He's just awful in this.

I thought the worst acting was actually in the spoken roles. Like the one where someone tries to calm down anxious crewmen by saying whatever is happening, the captain will tell them whenever he's ready. The guy had no facial expression and a nearly monotone voice.
It's fine to have actual servicemen doing lines, but couldn't they have done some auditions among the crew to find the best actors? Even if they ended up playing parts they aren't in real life, that's why it's called acting! It's not really impersonating an officer if you're just doing it on-screen.

I disagree simply because to me it adds some realism. It's one of the many things about this film that makes it less cookie-cutter. Great film!

I disagree. As human as our servicepeople are, these are people who have had calmness and coolness beaten into them since the first day at basic training. These are folks who know how to put it all aside - that is why they serve our country!
If anything, they do it for the man next to them.

the general crew in the mess hall [if that's the right term])
Messdecks. Halls are on shore facilities. We don't have halls aboard ships.
I joined the Navy to see the world, only to discover the world is 2/3 water!