Revealing mistake: Star Is Peeved: When Kel is eating the sugar cubes it is clear he isn't eating them at all. (00:07:50)
Revealing mistake: Cold War: Kel misses hitting Roger when trying to wake him up.
Revealing mistake: Mo Sweater Blues: When Kenan and Kel are using the high pressure hose to clean the sweater, if you look closely you can see that the sweater is pulled off the wall.
Answer: He's simply enjoying doing it himself. Especially since he likely believes he can do it better than she can.