When having a talk about deep matters and you don't want others to hear and abruptly someone comes to hear what your conversation is about.
1. James and Ryan were having a conversation about girls in their class and Sally came and totally talkblocked them forcing them to change the conversation and continue elsewhere.
2. Chris and Peter were chilling in their room talking about whether or not they would get baked but Peter's mom burst open the door leaving them to talk about other matters. She was a huge talkblock!