This works in two directions. I wholly agree - it's incredibly rude when they bogart your thread. On the other hand, like Brovo said, when they come in and literally just sit in monologue all day... Don't ALTER my plot - create and add to one for your character, play organically. Nobody does that anymore... Well, I don't think many did. If you're just going through the motions, not advancing something with at least a majority of your posts, then you're pushing the roleplay back. It's a balance. :p A difficult one for a lot of people, myself included.These have happened several times:
As a GM, when a player takes over your RP. Let's say you have plans for something. Huge plans, like a Big Bad, or a guy watching your every move. Then all of a sudden, a player takes over, and removes the tension completely. How am I to work with this? Like seriously!
As a Player, when you use common sense and logic, and get punished for it.
Yes, this happened.