To perform a "deverill" is to take a course of action that is greatly misappropriate to the situation one finds themselves in.
Lauren: Dev raped me.
Deverill is the act of gravely miscalculating the chances one would have of making it with the ladies. Such a mistake often occurs through excessive alcohol abuse or more simply being a peeny.
Wow did you just get with that lauren girl?
Nah i did a deverill...shes ran home...