I have to agree that gangsters aren't really nice guys. But as far as their reputation with outsiders, Costello's underboss Willie Moretti was considered approachable and friendly with strangers. During the Kefauver hearings, at the end his testimony he invited all the US Senators on the panel to come over to his home near the beach. I've also seen Longy Zwillman described as congenial and polite with outsiders.