Merkuri
Explorer
Oryan77 said:They step into the room and see the BBEG. The BBEG tells them to 'go away and leave his treasure alone unless they are interested in buying his wares from him' (he's sort of a merchant). The powergamer was already trying to interrupt me to let me know he's attacking. I ignored him until I could finish my dialogue. Then the casual gamer tries to ask the BBEG what his asking price is for his wares and as soon as he replies with his price, the powergamer interrupts me again to tell me he's casting a spell. So I tell everyone to roll initiative.
If he's actually interrupting you (or trying to talk over you or whatever) then I think you have a serious problem with that player, as a few others have said. If he's so keyed up to get into combat that he won't let others chat for a few moments then he needs to wake up and realize there are other people in the room.
You may want to have a group meeting to talk about how you want to make sure everyone is having fun, and that means that there will be times when combat is not the answer. Do not call the powergamer out or indicate that he is why you're making this speech, just let everyone know that things are gonna change a little. If he continues to ruin roleplaying moments take him aside and explain to him personally what you are doing and why. If he keeps doing it after that then it's clear he's just an inconsiderate person, and if I were in your position I would probably begin thinking seriously about whether I want to keep playing with this guy.
Subtleties may not work on him, if he's that into combat that he doesn't recognize or acknowledge that some people like other parts of the game.