Se ego certiorem facem, mihi tu delendus eres.

(Going from memory there. I hope I spelled it correctly.)

I have a patch from VX-4 at NAS Point Mugu that is all black except for red borders and the phrase in the title spelled out in red around its perimiter. I know what it’s supposed to mean: “If I told you, I’d have to kill you.” But – and I don’t speak Latin, so I have no idea if this is correct – it seems to literally translate to "If I made it a certainty to you, you will, to me (i.e., “in my eyes”), be deleted.

Okay, I can see how the literal translation makes some sense, but I don’t think it means what I think they think the Latin means.

What is the grammatically correct way to say “If I told you, I’d have to kill you” in Latin?

[sub]Disclaimer: I’ve had Latin classes at school for nine years totally, but it’s about a year ago that I stopped, so it could be a bit rusty.[/sub]

The phrase you’re citing seems to be pretty accurate to me, except for the fact that I’d say “Si te certiorem facerem…”. “Certiorem facere” means to inform somebody about something, but the “te” (you) should go in to make clear who’s informed. The “delendus eres” (“you would be to be deleted”) seems pretty euphemistic. I’m pretty sure the “facem” thing is wrong, but “facerem” should be a valid first person conditional form.
(Note: If you’re talking about a woman, it’s “delenda eres”)
But Latin is very rich in synonyms - there’s certainly a lot of ways to express “If I told you, I’d have to kill you.”

“Delendus” = “must be destroyed” (gerundive of obligation, IIRC). Most famous example, delenda est Carthago, “Carthage mut be destroyed” - Cato’s oft-repeated effort to influence Roman foreign policy.

Forget what I said about the euphemism. “Delere” plainly means “to destroy.”