As moms, the reason behind the bad behavior is often as important for us as the bad behavior itself, but with a gifted child, they're often perceptive enough to understand this about us and manipulate us into accepting bad behavior and into making excuses for their inappropriate responses to stressors.
After raising two kids who are grown, I'd say the one thing that helped the most was drawing a line that I refused to accept if they tried to cross - and name calling and disrespect were on the other side of that line. When they crossed it, I sucked in the hurt and responded swiftly, severely and consistently. (And by severely, I mean in the level of reaction/punishment - not escalation.)
I often cried later, hurt that they'd been unkind, but they needed to know I was parenting them and not responding to their bad behavior. It usually stopped it in its tracks.
My older son went through a particularly rough period in mid school, and it got to the point that I let him know that our "obligation" was to clothe, feed and provide medical for him. Above that, it was all perks. We took away his gaming things, then his iPod (one of the first gen at that - smile), and it wasn't until I informed him that if he couldn't learn to respect and appreciate what he had, he would come home from school to find he'd lost his furniture, all but a single change of clothes and his door. They were perks he'd have to earn back.
He became a model of respect over night.
And so the only advice I have for you is not to react in mild increments. If it is something you do not want to ever tolerate (and what he thinks he can do to his mother will be what he'll do to his wife some day), then make sure he knows by the punishment that the price is not worth the bad behavior.
Hang in there. Parenting sometimes really sucks, but if we hang in there, we weather the storm and come out the other side with kids who respect and love us - and that we respect and love.
