Someone who acts like they own the place and that the whole world revolves around them. They look after number one, and everyone else is low on thepriority list. If you know the arsehole well, often even just their presence can make you feel small and insignificant, and generally they treat you like something they stepped on.
He just strolled in, ignored the shopassistant, took what he wanted, threw the money on the counter and left. What an arsehole.
It is also used to describe a member of society who is thoroughly useless or who's actions add to the problems of others.
For example a Social Security Medical Officer who issues a false medical report in order to cut the disability payments of the most vulnerable members of society can be correctly described as an Arsehole (note the use of the capital A).
