"Whose testicles are these?" I'd ask, my mouth curling in a coy smile.
I'm assuming that if someone offered me a plate of testicles, that they are the cooked kind from an animal known to have their testicles consumed by man. If that is the case, I would eat said testicles.
If the testicles were, like, fresh, like recently cut off a thing, I'd decline to eat them. If they were human testicles, I'd also decline, unless they were the testicles of my enemy and they were prepared the way testicles consumed by man are normally prepared. Hopefully with a sauce. Or maybe risotto.
To reiterate, I would eat the testicles of my enemy. So look out, fuckers. Don't be making an enemy out of this guy. He'll chef your balls up nice.
Short Answer: I might ask why they brought me a plate of testicles when I ordered the ceviche. Ooh! Ceviched testicles; thinly sliced, raw, with some lime juice. "Sir, I have hear the ceviched testicles of your enemy." Can ceviche be a verb? Did I just lose half of my audience? I see.