They can, but at the same time, I don't want to enforce a nanny state where everyone has to be perfectly polite at all times - Mafia gets heated and I believe people should be allowed to express that. Obviously, slurs are a no-go, but general profanity (depending on where it's directed) is fine. I don't really want this place to be like Mafia Universe, where oftentimes you are more mindful about what you're saying than you'd like to be.
To use an issue you've brought up, being funneled for several days can certainly be frustrating, but I'm not going to say "you can't do this" because it's valid within the boundaries of the game. Obviously people should try to be mindful where they can, but ultimately it's on the person getting frustrated to remove themselves from the situation if they feel pile they aren't able to control their emotions at that point.
That of course, doesn't give anyone license to berate a player over and over again because they feel their objection to the player is justified.