One of the funniest Grover moments for me was the waiter one where Fat Blue kept changing his mind on his order (first he wanted 2 strips of bacon and 2 eggs, then 3 strips of bacon and 1 egg). When Grover brought this food to him, he smiles and says, "Uh, you might think this is gonna sound funny but ... I changed my mind again!" And Grover (quite perturbed by now) says, "Oh I do not think that sounds funny at all." I love the way Frank Oz said that! (as well as the way Jerry Nelson said the preceding line! )
Of course at the end, when the customer changes his mind yet again and wants lunch ("Two hot dogs and two pickles") Grover loses it in the kitchen as we hear him screaming to Charlie and breaking dishes. A great skit, as so many Grover ones are.