When I was a kid, I used to find Jerry creepy, but he just looked like a ordinary guy. But Billy I found creepier, he had a really evil smile and his eyes would go to slits when he smiled. He always scared me!
Jerry is supposed to be seductive so he shouldn't seem creepy (well, much, he is a vampire). Billy is a minion and traditionally they shouldn't be better looking than the guy the serve.
I think that may have been the point. Jerry was supposed to be charming and attractive. Billy is suppose to protect his master by whatever works including creeping out nosy people like Charlie or being pretty friendly like to the cop. Creeping Charlie out only helped make Charlie look foolish when he is so obviously "a nice guy".