Mr. Cat and Olaf seem to despise each other and they are both on very bad terms with each other.
In "Let's Play Gentleman Burglars", the first episode where Olaf appeared, the first thing Mr. Cat did was to kick Olaf into the air when he tried to get him to bow down to him. Later in the episode, Mr. Cat (along with Quack Quack) leaves Olaf locked in a car. These actions, along with the rest of the main four's antics, finally prompt Olaf to attack them near the end of the episode. In "Let's Play Household Hazards", Mr. Cat tries to shoot Olaf with a bazooka because he tried to hurt Kaeloo, but Olaf calls his robot Serguei to get rid of him. In "Let's Play Horse Riding", Mr. Cat successfully cheats Olaf out of 6000 dollars, and the latter yells at him for cheating but then leaves. In "Let's Play Frosted Christmas", Mr. Cat gets angry at Olaf for kidnapping Quack Quack, and "Let's Play Frosted Christmas - Part 2" had him even try to beat him up.
Olaf treats Mr. Cat just like he treats everyone else - with a lot of contempt and as though Olaf himself is better than him. In "Let's Play Gentleman Burglars", he gets angry at Mr. Cat for continuously mistreating him and finally attacks him (and the rest of the main four, who were also not treating him very well). In "Let's Play Frosted Christmas - Part 2", when Mr. Cat tries to beat him up, he freezes him alive and captures him in a giant jar.