Well, when I saw the RENT tour there were people in the front row who were standing up and singing. In fact, in an interview Lea Salonga said that she couldn't really judge RENT because it was so hard to hear the music with the rowdy audience. I know someone who saw people standing up on the chairs during RENT. From my experience, a lot of the fans treat it like a concert.
Of course, that was before Wicked. Maybe now RENTheads have calmed down. But when I saw the movie it was the first showing, and everyone besides me--mostly teenagers, may I say--was acting in a similar fashion: singing along, dancing, calling out, etc.
As for Phans, it depends. While I hate the show, I do love the novel so I know and am friends with quite a lot of Phans; I was actually surprised by how most admit that it's not a very good score, and it has awful lyrics, but they like it anyway. And I'm fine with that. What exasperates me about Phans is, as many have said, a great deal of them refuse to acknowledge any other show out there. Of course, eventually they usually do. From experience, I've found that they usually move onto another more mainstream one, like Les Mis. And, well, I think a lot of us started out with Les Mis, even though it may have been much earlier (for me, it was in the first grade, for instance.) So we can't really roll our eyes--tempting though it may be--if they're trying to broaden their musical horizons.
As for during the show, when I saw Phantom I had no trouble with the audience. Online is probably where I've gotten more of a negative experience with them. But, well, there are plenty of phans who are intelligent and have diverse taste in musicals. A lot make fun of ALW, especially after he approved the casting of Emmy Rossum and Gerard Butler.
Honestly, I'd say that the scariest group can be the Sondheim fans. They're usually intelligent, yes, but they can also be quite intimidating and snobby. If you dare to say that you dislike one Sondheim show, quite a few will just go "oh, you didn't understand it." They can accept no flaws about him.
Then again, I guess I'm sort of similar about Jason Robert Brown. We all have our fangirlish/boyish tendencies.
Jimmy, what are you doing here in the middle of the night? It's almost 9 PM!