I think it's very rude. It's calling him a wimp and that you have the control in the relationship.
Although it may have been said in jealousy, usually is.
The best comeback is "There are worse things to be whipped with." ;D
Usually guys say use that term jokingly, meaning that they don't spend as much time with their "boys" because they are in a relationship. I doubt he meant it to be rude if they are friends.
So wait was that a rude commeny he said? Im.cunfused
Someone who is "whipped" does not stand up for themselves and will do anything you say. A lot of people throw around that term very loosely though, so you can take it as you see it.
Oh the ***** why starts with a p and is another word for vagina