EMILY: You brought us used dessert?
LORELAI: It’s not used. It’s left over.
EMILY: How nice. I’ll just put it in the kitchen next to my half-empty box of Cheer.
Cheer is a brand of laundry detergent sold in the US and Canada, and made by Procter & Gamble. It has been sold since 1950.
It’s very unlikely that Emily really keeps laundry powder in the kitchen, or that she would store cake next to it. She’s just being nasty. Most people are prepared to be magnanimous and conciliatory when they get everything their own way, and are proven right in a disagreement. Not Emily.