Cleo: "I know! It's a pizza!" (chews flat beach ball) "Yech. Definitely not a pizza..."
Pretty much the whole episode "An Itchy Patch", especially this scene:
Veteranarian: He seems to have a rash. Clifford:(Oh, Crap face)
From "Flood of Imagination":
Clifford: Okay, so if we're going to the ogre's castle to rescue Emily Elizabeth, we'll need to bring a few things. Like a picnic. Cleo: And some games! T-Bone: And CAKE! Clifford: And some maps. Cleo: And an inflatable swimming pool! T-Bone: And CAKE! Clifford: And gas for the car. Cleo: And 27 pogo sticks! T-Bone:And CAKE!