Etiquette of interrupting the DM?

Suppose I want to take an action in the middle of a scene described by the DM. E.g. a villain is monologuing, and I want to surprise attack them or try to steal something while everyone is distracted. I feel like I need to interrupt the DM before the moment for action passes, but I don't want to be rude or annoying to the DM. What's a tactful way to go about it?