When you're GMing, what is the best way to approach someone with a character that is too cliche? For instance, if someone has a Drama King/Drama Queen character, a character with an overly-tragic backstory, or a character whose personality or past does not make any sense. This has always been a problem for me whenever I organize group roleplays, and I'd love to have a quality casual role-play without bad writing skills and all of the common tropes that make characters almost unbelievable. Any advice?

Thanks!