How to get someone to stop talking
Try dropping anything (that won’t break, like keys) if you find yourself in a conversation with someone who simply won’t let you say a single word. You may take control of the discussion and say what you meant to say because it will interrupt them and cause them to pause for at least a moment.
This meets your aim without you having to awkwardly interrupt the other person to get them to stop talking, or worse, tell them to let you talk.
