That is not a common thing in workplaces. Interrupting someone who's speaking is rude, plain and simple, in any context. People that talk over each other, to be blunt, have no manners. Are the discussions important to your work, or just social though? If work-related, they need to be managed in a setting where everyone has the chance to speak and be heard. I would discuss this with your manager if it's work-related, and hopefully he/she can provide an environment that's managed and not chaotic babble going back and forth. Also, there are books and resources that might help you be more assertive and confident in situations where you have to jockey for attention. There aren't many times that happens, but in competitive business, it does happen. Everyone is looking out for #1. I'd add that people that interject all the time are poor listeners, which is a problem in business(and life). If all they're doing is thinking about the next thing they're going to say to the point they can't even hold it in, then they certainly aren't paying due attention to whoever is speaking and the topic and giving it diligent consideration.