I have over the years participated in many kinds of tabletop gaming groups. Not only is playing those games fun, of course, but the social interaction with people is, perhaps, even more important. It's nice to have conversations and social interactions with a group of friends.
However, there is one sort of person that ruins that second aspect. And I don't mean that they are somehow obnoxious, or malicious, or behave in a reproachable manner (such as saying improper things, trying to cheat or take advantage in the game, or anything like that). They are often good people, with no ill intention of any kind, who participate in the group in earnest, because they like the game and the people. However, they have one personality trait that basically ruins the social interaction aspect of such a gaming group.
And it's that they seem to have some kind of pathological need to be always speaking, even if it means constantly interrupting others. Having a nice light group conversation is basically impossible when that one person is present, because he will always butt in into any conversation, and will very often interrupt people and not let them speak, and almost never let two other people have a back-and-forth conversation between themselves without him interrupting it. Even if you are talking directly to him, he will most often interrupt you mid-sentence, and not let you finish.
It has been countless times that I have arrived to a playing session early, and then other people start arriving, and we start having really nice and relaxed smalltalk and back-and-forth conversations about diverse topics, and it's all really relaxed and nice, and everybody can say what they want, and tell their little anecdotes eg. about what happened to them the other day, or what happened in the news, or about some curious story in some online publication, or whatever. Others will listen, and then express their views on the subject, almost never interrupting each other. It can be really nice social interaction between people.
And then that one person arrives, and the mood changes completely, because everybody just knows that the nice social interaction and the small-talk is essentially over. That person will just overwhelm every attempt at conversation, and nobody will have a good chance anymore at telling their anecdotes and stories and opinions, without being interrupted. Conversations will almost never lead anywhere.
And the thing is, as said, that person is not obnoxious, or having ill will, or impolite per se (other than interrupting people when they are talking), and he is genuine and enthusiastic. And it's not like that person has some kind of developmental defect or unusually low IQ; quite often he will be quite smart, intelligent and experienced, and what he says may not be especially stupid or cringeworthy. Everything he says may be completely adequate, logical and smart. It's just that he has this little personality trait that makes him, probably unwittingly, so pushy and constantly interrupting people, and essentially destroying any possibility of comfortable nice smalltalk, and expressing your opinions and stories without being interrupted.
Quite often he also tends to have a very loud speaking voice, so he overwhelms others just by that. And no, telling him not to interrupt will not help. He doesn't seem to learn, ever.
The annoying thing about this is how prevalent it seems to be. It's not like one person in a thousand, and the chances of having such a person in a random gaming group to be infinitesimally low. It seems like about every other such group has somebody fitting that description, more or less.
It becomes even more hopeless when there is more than one such person in the group. You can just forget about having any sort of conversation with anybody. It just destroys one of the most important aspects of tabletop gaming: The social interaction between the players.