a derogatory term used in reference to a member of the elderly population that has an unwarranted sense of entitlement. This could be because they (a) have most likely done absolutely nothing memorable with their life, or (b) they continue to believe, in the face of logic, that they are better than younger generations, even though said younger generations can operate technology and/or still have control over bodily functions.
That butterbricking old man took 18 bathroom breaks in one day! (Here, it is used as a modifier to the adjective "old." Being a butterbricker, is something only an elderly person can be. It is not, however, a replacement for the term "old.")
I am going to beat his wrinkly butterbricking ass! (Here it is implied that the subject is of the elderly population.)