"What's Up Doc" is one of my favorites - it shares my comedy niche with Galaxy Quest, Monty Python and the Holy Grail, The Blues Brothers, and The Big Lebowski.
IMO - though she was just in a supporting role, Madeline Kahn was the true star of the movie and totally deserved a Best Supporting Actress Oscar for her outstanding portrayal of Eunice Burns. Her performance was so critical to the movie. But comedy historically isn't valued by the academy, so she wasn't even nominated.
I love the convention dinner scene ("Who is that dangerously unbalance woman?") where she's dragging the woman holding on to her leg, while she's wildly singing her purse to fend off everyone around her. Then, when they drag her out, wailing and crying, she drags her heels back and forth, leaving squiggly heel marks on the floor.