He knows a villain monologue when he hears it.
Cisco has steeped himself in comic books since childhood. The tropes swim in his blood. So when Harrison Wells starts off with the mocking applause, he knows what this is.
(Even though he tries not to.)
This is the moment that the villain reveals himself for what he truly is, what the readers have known, what the characters have missed even when it was right in front of their noses. All those inconsistencies. They all add up. Somewhere, readers are groaning, "Finally, you dummy, finally you see!"
He also knows something else.
He is not the hero.
The hero is the only one who ever survives the villain monologue, because he's, you know, the hero. But Cisco is not the hero. He's the sidekick, the plucky comic relief. He makes the toys, calls in the hero for actual battles, and stays out of the way. Because he's not the hero. He doesn't have the jaw or the height or the gravitas.
(To be fair, Barry's only got two out of three himself, but he has the speed, so that makes up for a lot.)
Now, Cisco knows that his role has changed.
Now, he's the innocent sacrifice. The one who dies because the stakes have to be raised. You have to know how truly bad the villain is. The hero must suffer great loss to propel him toward the final confrontation. It's a classic.
Ridiculously cliched, too, like most classics. But right at this moment, Cisco can get behind the argument that it's a cliche because it works, oh how it works. Barry will take this guy down, will take him apart, for what he's about to do. This is the fucking line, right, man? This is the line you do not cross with the hero. You don't fuck with his friends.
With every cell in his body, Cisco wants to be there to see it.
He says, "I can help you," in desperation, knowing that with the statement he's transforming himself from the innocent sacrifice into the craven turncoat.
(Or possibly the wily double agent, working against the villain from within. Yeah. Cisco can respect that.)
When Harrison Wells - Eobard Thawne, good goddamn, is that a villain's name or what - smiles at him, Cisco feels his brief fantasy of secret heroism fall to ashes. He looks at the vibrating hand that will kill him and some part of him that's not entirely connected to reality right now thinks, That's actually pretty awesome.
The rest of him looks away, at the ground, unable to stop the tears, nauseous with fear.
You always think you're going to go out like a badass, that you'd spit in the villain's eye when he shoved his sword through your heart. But the truth is you stop caring about pride or dignity or honestly anything but keeping your heart beating when you see that weapon coming for you.
Somehow, he'd never thought how much a tired cliche would hurt.