Other than the sociopath (and I’d say we need to revisit just how a sociopath or psychopath is seen by the med and psych communities,) it doesn’t matter if one has to ramp up to be pleasant or it comes naturally. Bottom line: be pleasant, however you get there. One can learn the skills to come across as interested. You can learn to say hello and shake hands, the skills in interacting. Then, afaic, go home and brood.