Ladd Russo from Baccano. Now I know that when you think, about it isn't every one from Baccano a villain?
After all you have robbers, mafia gangsters and insane immortals, however out of all of these Ladd Russo stands out, why? Simple he's batshit fucking crazy. He has an extreme love of death and is most happy when killing, especially when his victims beg for their lives.
That's it for my 20 villains, definitely not the kind of people you would want to go drinking with.