In all the years I have DMed, I don't think I have ever had a BBEG successfully intimidate a PC. I don't mean via the intimidate skill. I just mean that, when a powerful NPC confronts the party, none of them ever show the respect that he deserves. The PCs respond with smart aleck responses and general disrespect as if the evil being standing before them is nothing more than a homeless man asking for change.
It doesn't matter how I roleplay him or how I describe him, if he is a bad guy (even many levels higher than them), they will mouth off to him. Most of the time, it is done in an immature way to boot.
So how do you handle this as a DM? Let it happen and shrug it off, letting the BBEG look like a complete tool in the process? If I were to roleplay the NPC appropriately, he'd just slaughter the disrespectful idiot and be done with it, turning to the other PCs and saying, "anything you want to add?" I just figure that doing so would eliminate part of the fun for the players since it seems to be an enjoyable pastime to belittle anything that a powerful BBEG would say. Still, it does make me feel like the bad guys are pushovers when I'm trying to make a scenario feel a bit scary in order to put the PCs on edge.
It's not that I expect the PCs to cower in fear. Heck, most protagonists in movies do disrespect the bad guy during his monologue. But just once, I'd like to see the players biting their tongue. I just can't figure out how to do it.