First off, the show is called "Kid vs Kat"; Coop and Kat are supposed to hate each other. The main reason Coop and Kat don't get along can be found in the episode, "Let the Games Begin". During the episode, we can see Kat already does not like Coop, but what really seals the hatred between them Is when Coop takes Kat's collar and accidentally causes it to blow up, destroying the teleportation feature along with it. After the collar explodes, Kat, from that point on, will believe that Coop was the one who stranded him on Earth (This will become clear by the end of the series). From this point on, we not only see Kat trying to get home but actually try to harm Coop as well. Rumors say that Season will have more episodes of Coop and Kat actually working together more often; maybe will finally abandon his attempts to seek revenge on Coop and enlist him in his quest to return to Planet Catnip.