Are casey and derek dating in real life
They are considered to have the most UST in the show, partly due to the fact that between them everything is usually a competition.
They also show a protective"She's a good girl, a perfectionist and people pleaser. She's looking for love, he's looking for his next bimbo.
Dasey shippers often "hate" the characters' actual girl/boyfriend in the show (Max and Sally in Season 3, Truman in Season 4).
It was especially true for the character Truman in Season 4 as well as some displeasure at Emily becoming Derek's girlfriend in Season 4.
Canonically, they fight and prank each other a lot, however despite all of that - deep down they care for one another, which is one of the main reasons fans ship it so much.