"Accepted" might mean that nobody cared or thought anything of it. Or maybe it might have been considered taboo, but given a pass because "he's a Duke, are you gonna tell him he can't do that?"
Well, the Wars of the Roses were in that period, in which you had Nevilles and Percies ambushing each other along the borders, lords rebelling against kings, disorders in Wales, lords obediently passing acts of attainder and repealing attainders passed by the last faction to control the throne (removing titles, seizing property, and outlawing on a mass scale without even the pretense of a trial), ... Even in peaceful times, you had things like Gloucester and Clarence teaming up to get their mother-in-law declared legally dead in order to grab her lands.
But let me ask: do you mean things farther down on the scale than things that get into history books 500 year later, like some earl seizes a church or something?
Up until the early 20th century peers of the realm were not tried in a judicial court for crimes, but by the house of Lords. There were some interesting results which eventually lead to the house of Lords deciding that they should not sit in judgment of themselves.