The Cat Fight between Sylvia and Miriam in Reno, after Sylvia learns that Miriam is the one her husband is seeing. Doubles as a Crowning Moment of Awesome and Laser-Guided Karma as it serves as a form of comeuppance on bitchy Sylvia. The icing on the cake is Sylvia's freak-out after the fight ends, when she starts breaking stuff and screaming how she hates everyone, and Lucy says she's got "the hi-sterics".
Sylvia: How much did my husband pay you?
Miriam: I made Howard pay for what he wanted. You made him pay for what he didn't want!
Mrs. Morehead clearly doesn't think much about Mary's choice of friends. Right after they leave, she charges out of her room with a perfume bottle.