Barely not serious here

The worst decision Donny Dunn made in the entire series was right at the end of S01E07 when he ordered a Double Vodka & Coke.

Vodka and Coke???? That makes zero sense. You mix whiskey and bolder spirits with Coke. Why would you mix Vodka and Coke? It's a better match for juices and you can use soda water for bubbles. I'd even take Sprite and say it's acceptable.

I see no clearer evidence that Donny Dunn hates himself than his decision to order a Double Vodka & Coke.