To me, lowering a grade for discipline issues is a way of not confronting a problem, and from what I've seen, it doesn't work.
I tend to attack attitudes at the door, literally, if necessary.
In this case, "rude" is just another way of saying "disrespectful." I'm also a proponent of reality therapy, and making a student aware of the natural consequences of disrespect, in life. S/he isn't simply disrespecting me and others, but himself, the institution of free education, his parents, everyone else who is working for his success, etc, etc.
Needless to say, no, I've never lowered a grade for an attitude. I've never had to. If a good student has a bad attitude, it is pretty easy to get to the root of the problem and help the kid change his behavior. But more often than not, in my experience, the kids with bad attitudes end up with low grades anyway, because the attitude trickles into everything.
Now, if an entire class is displaying disrespect (most often happens for me in honors classes, where the sense of intelligence and entitlement = talking whenever they want), I find ways of making classwork impossible to complete if they want to sit around and talk. It makes for a lot of work on my part, and often really creative lessons, but usually nips class behavior in the bud.