I think the concept of murder and merciless killing would be a pretty valid answer, but then again, killing is pretty cliche - not that its a bad idea, because it could be the best when it comes to evil.
Among the best bad guys, I believe, are those bad guys that people actually respect... >.>
Ok I know it sounds wrong to respect a bad guy, but I'm thinking in more of a respect induced through intimidation kind of thing.
Sure you can have the maniac that goes around murdering innocents, but they dont make much of an impact, or at least, people disregard their intimidation more because they're just crazy.
I reckon he should be confident, highly confident, and I think he should feel like he is just above everyone else. Disrespectful, rude, selfish, all add to the effect.
On the other hand, sometimes the evil characters make a massive impact when they're the opposite to those traits. For example, to have a kind and respectful man ruthlessly kill someone out of pure malice can really twist his character. But then you'd really have to make his personality stand out, make his character stand out.
I reckon you should just make him stand out a lot. Be it through the contrast in his actions and personality or his appearance or his attitude. Thing is with the rockets, they're disrespected because of their sheer stupidty, they're regarded as comical, like you said. To have the caracter stand out and be respected is more of a believable bad guy.