Continuity mistake: When Kel initially hits the wall with the mixer whilst they're making a cake the picture falls down, however when he chases Kenan over to the same wall with it seconds later, the picture is back on the wall again. (00:14:35)
Revealing mistake: When Kyra goes upstairs after kissing Kel in the opening scene, it's clear the stairs don't go any further as you can see her shadow on the wall climbing down backstage.
Character mistake: In the flashback of Mr. Mac Fist hitting Roger in the eye, the fist hits Roger in his right eye. Once the flashback ends and goes back to the present Keenan and Kel, Keenan says "My dad couldn't see out of his left eye for 2 weeks."
Aw, Here It Goes To Hollywood (2) - S4-E9
Continuity mistake: When Kenan and Kel are chased out of the shower by David, the clothes that he's wearing are completely dry, despite the fact he was just in a running shower.
Continuity mistake: Roger is building Kyra's castle out of sugar cubes. He starts to put two cubes on top, but then the cubes changes from two to four and then back to two again in the next shot.
The Raffle - S3-E3
Visible crew/equipment: When Kenan and Kel are in the back of Rigby's, some stage lights are reflected in the fridge. (00:08:45)
Continuity mistake: Mo Sweater Blues: For the amount of water Kel splashes on Kenan the wet patch is way to big.
Continuity mistake: Mo Sweater Blues: When they arrive at the restaurant the stain on the sweater has changed shape.
Answer: He's simply enjoying doing it himself. Especially since he likely believes he can do it better than she can.