Margery Pinchwife's letter scene is one of the best, along with the bone china. SHE STOOPS TO CONQUER's Mrs Hardcastle, although she's got precedents like Lady Wishfort, has to be the first "camp" character in literature. Every time she comes onstage I laugh myself silly.
I also like Vanbrugh's THE RELAPSE; who couldn't love a country bumpkin named Hoyden Tunbelly?