Have you ever known someone who was obsessed with talking?

They just talk and talk. It’s always very one sided because any small contribution you may make is fielded and immediately turned into a “similar” experience they have had.
They ignore subtle social signals that the conversation is over…subtle, like you have your coat on, purse over your shoulder, keys in hand, hand on the door….and they may very well get up to come stand by you to continue talking because you moved away from them when you walked to the door.
Someone who does that stream of consciousness conversing (to themselves, pretty much) for an hour and in the process some very inappropriate and STRANGE thing may come out, and they continue on without pause.
Or someone may make some small comment about a medical condition they have—maybe they refuse the offer of a cookie because they have diabetes—and that comment may cause this other person to launch into a long winded and totally inappropriate dissertation about issues with, say, their digestive tract with no attempt at talking quietly or privately. In fact, they seem absolutely certain that everyone is very interested in the details.
Have you ever known someone like that? Can anyone explain this?