Police detectives who wear either fancy and probably expensive clothes (often with stiletto heels in the case of women) or some sort of hip looking casual clothes. On top of that, these detectives often work in very sleek and very modern look police stations, not at all what real police stations probably look like inside.
The two worst offenders of this trope are Castle and Lucifer; Detective Beckett, while living in at tiny apartment always seemed to be wearing designer clothes that I highly doubt a police detective could afford and/or would wear as work clothes, and then there's Det. Esposito with his hip urban clothes. In the case of Lucifer, Detective Decker dresses a bit casually for what I'd imagine how a real LAPD detective would dress and the precinct office is pretty slick looking, very ultra modern, like something out of a Google or Apple office.