What's really amusing is that he has Factual Determination Analysis. Could come in handy if we act correctly.
Anyway, I'm gonna try to stunt this. I was initially thinking of a Malfean excellency, but trying to take him alive may count as showing restraint, which makes it inapplicable. (I was thinking something along the lines of boasting about actually being a Prince of Dragons, not a vampire. Though, that could be applicable.) We could go for a TED excellency by pretending to be a vampire and yelling about how he is the same as us, but that seems like it'd make more trouble when it comes to convinving him. I'll give both Oramaic and Ophidian options a try. The beginning of each stunt should be mostly the same anyway.
Ophidian:
You sigh at the Infernal's words and reach behind your back, activating the concealed weapon on your fist. This man is such a fool, unlike yourself. Still, as annoying as he is, it's in your best interests to subdue him, however you can.
"Yes, I am most certainly one of those monsters that you fear! How sad for you then that I have come to tell you that you are one as well!"
Even if your shocking words don't do the trick, your hidden shocking weapon might...
Oramaic:
You sigh at the Infernal's words and reach behind your back, activating the weapon placed unexpectedly on your fist, brought along specifically for tonight. This man is such a witless fool, compared to yourself. Still, best to speak with confidence here.
"You fool! Your singular expectations cannot possibly grasp my nature! For unlike an easily slain vampire, I am the one and only Prince of the Forgotten Dragons!"
And if demoralising words won't do the trick, perhaps a magical version of the same will....
Honestly, I think I like the Oramaic stunt better. It doesn't involve giving him an implication we'll have to correct later, and the Ophidian stunt kind of dances on the line between truth and lies, since even though neither of us are vampires, both of us are Infernals. Might be a case of trying for too much in the way of excellencies. Plus, between his stupidity and possesssion of Factual Determination Analysis, he might well choose to interpret things in the most inconvenient way possible.