a publicly acceptable way of calling someone a jackass. someone who recently has done something stupid and deserves to be called a jackass, but there are people around that wouldn't appreciate that and so you simply call them a jackaloon.
Any one adult person who engages in acts of a mentally retarded child. Someone who clearly demonstrates a lack of commitment to maturity and the responsibilities that come with it.
Dr. Doback in Step Brothers to his 40 year old son living at home who cant get a job or act like an adult: